[Theory] The definitive proof that Future Goku NEVER learned Instant Transmission

[vilker]

I am tired of seeing fans and guidebooks claim that Future Goku knew Instant Transmission (Shunkan Ido) just because Present Goku said "I was about to use it." That is a lazy explanation that creates massive inconsistencies.

If we look at the manga's logic strictly, the evidence proves Future Goku never learned the technique.

Here is the irrefutable breakdown backed by the Manga events:

1. The "Spy Robot" Paradox (The Smoking Gun)
This is the most critical piece of evidence that destroys the official narrative.

THE FACT: We know Dr. Gero’s Spy Robot was present during the Frieza invasion to collect cells and combat data for Cell.

THE SCENARIO:

If Future Goku used Instant Transmission: He would have appeared instantly in front of Frieza. The Robot would have recorded this "teleportation" data. Consequently, Cell would have this data in his bio-computer.

THE REALITY IN THE MANGA: Cell does NOT know Instant Transmission initially.

When Goku uses the technique against Imperfect Cell, Cell doesn't understand anything.

Crucial Point: Cell explicitly states that he learned the Instant Transmission only AFTER he self-destructed on King Kai’s planet and regenerated. He says: "I was able to learn Goku's teleportation technique as well."

The Conclusion: If Cell had the data from Future Goku's fight against Frieza, he would have known the technique from birth (just like he knew the Kamehameha). The fact that he didn't know it proves Future Goku never used it against Frieza. He fought him physically from the start.

2. Trunks’ Reaction (Manga Chapter 336)
When Present Goku returns and demonstrates the technique to the Z-Fighters:

Trunks is genuinely shocked. He stares in disbelief.

The Logic: Trunks was trained by Future Gohan. If Future Goku had saved the Earth using a "miraculous teleportation move," Gohan would have told Trunks about it. It would be a legend.

The Fact: Trunks has zero knowledge of it. This implies Goku arrived in the Future via the spaceship, fought Frieza the "normal" way, and died of the heart virus without ever showing or mentioning teleportation.

3. Bulma’s Log and the "Empty Ship"
In the Future Timeline, Bulma tells Trunks the exact time and coordinates of Goku's landing.

The Problem: If Future Goku used Instant Transmission, he would have arrived hours before the ship. The ship would have landed empty.

The Inconsistency: Why would Future Bulma record the ship's landing time as the "moment Goku returned" if Goku had already been on Earth for 3 hours? It makes no sense.

The Solution: In the Future, Goku didn't teleport. He rode the ship all the way down. He stepped off the ramp at that exact time. That is why Bulma recorded it.

4. The "Butterfly Effect" Confirmed by Toriyama (Via Trunks)
Some fans argue that the timeline shouldn't change that much. But Toriyama tells us explicitly that it did, and he tells us why through Trunks' dialogue.

The Fact: Trunks discovers Cell's Time Machine and realizes it arrived in Age 763—exactly one year before Trunks himself arrived to kill Frieza.

The Quote: In the manga, Trunks explicitly wonders why the history is so different (different Androids, different power levels). He concludes that the arrival of Cell's time machine one year prior is the root cause.

The Implication: Toriyama is literally speaking through Trunks here. He is establishing that the timeline bifurcated in Age 763, not when Trunks killed Frieza in Age 764.

The Result: Since the timeline split in 763 (while Goku was still in space), this "ripple effect" altered events in the universe, including Goku's training on Yardrat. In the original history (no Cell arrival), Goku rushed back or didn't perfect the move. In the new history (Cell arrival), the timeline shifted, and Goku mastered it.


5. The "Egg Regression" was a deliberate Plot Device (Meta-Analysis)
Finally, ask yourself: Why did Toriyama write that Cell had to revert to an egg because he "didn't fit" in the Time Machine?

The Narrative Excuse: "He was too big." (Weak excuse).

The REAL Reason: Toriyama needed a way to insert a divergence point years before the Androids arrived.

By forcing Cell to revert to an egg, he necessitated a 4-year incubation period. This forced Cell to travel back to Age 763, not 767.

This specific date (Age 763) is the key. It places a foreign entity in the timeline before Goku returns from space.

Toriyama created this convoluted "larva buried for 4 years" plotline specifically to fix this loose end. It creates the necessary background noise (Butterfly Effect) to justify why the history diverges so drastically, allowing Present Goku to learn a move (Instant Transmission) that Future Goku never had the "luck" or circumstances to master.


Summary
Stop calling it a plot hole. It is a timeline divergence. Future Goku: Arrived by Ship. No Instant Transmission. Robot recorded a physical fight. Cell doesn't know IT. Present Goku: Mastered Instant Transmission. Robot recorded the IT (implied, though Trunks intervened).

This is the only theory that fixes Cell's ignorance and Trunks' shock without breaking the story and make sense Bulma storing ship's landing in Trunks' watch.

[dbgtFO]

Yes, the Goku arrival time always rubbed me the wrong way thanks to everything you mention here.
Bulma should have given Trunks all the correct info, so it wouldn't make sense that she somehow neglected to tell him about Goku's teleportation, if that was how he came back and defeated Freeza and co. on Earth.

Only way would be if Toriyama was setting up this to be more conventional time travel, where Trunks was always the one to kill Freeza, so Bulma did not give him that info, so he could interfere on his own

[vilker]

Yes, the Goku arrival time always rubbed me the wrong way thanks to everything you mention here.
Bulma should have given Trunks all the correct info, so it wouldn't make sense that she somehow neglected to tell him about Goku's teleportation, if that was how he came back and defeated Freeza and co. on Earth.

Only way would be if Toriyama was setting up this to be more conventional time travel, where Trunks was always the one to kill Freeza, so Bulma did not give him that info, so he could interfere on his own

You are confusing a "Time Loop" with the Multiverse Theory, which is how Dragon Ball actually works. There isn't just one future; there are at least 4 distinct timelines.

This is the definitive proof that validates my theory. Let me break down the timeline logic step-by-step:

TIMELINE 1: The "Original" History (Where Imperfect Cell comes from)

The Scenario: This is the original, untouched history. No Trunks has arrived yet, and crucially, NO Cell has arrived from the future either.

Age 763: Since no Cell traveled back to this timeline, there is no "Time Machine Egg" buried underground. The timeline is "pure."

The Event: Mecha Frieza arrives.

Goku's Return: Since there is no "Butterfly Effect" caused by a future intruder (Cell), Goku returns exactly as planned: via Spaceship. He fights Frieza physically. He does not use Instant Transmission because he rushed back or didn't learn it.

The Consequence: Dr. Gero's Spy Robot records a physical battle.

The Result: The Cell created in this timeline (the one who later kills Trunks and travels to our show's timeline) is born without the data for Instant Transmission.

TIMELINE 4: The "Main Series" History (What we watch)

The Scenario: This is the timeline we watch in the anime/manga.

Age 763: Cell (from Timeline 1) arrives and burrows underground.

The Divergence: The mere presence of this future entity (even as an egg) creates a ripple effect (Butterfly Effect) before Goku returns.

Goku's Return: Due to this subtle alteration in history, Goku's circumstances on Yardrat change slightly. He masters the Instant Transmission. He prepares to use it (as he told Trunks), but Trunks intervenes.

The Conclusion: The fact that Imperfect Cell (who comes from Timeline 1) doesn't know Instant Transmission proves that in his original timeline (Timeline 1), Goku never used it. If history were a simple loop, Cell would always have that data. The fact that he lacks it confirms that Future Goku (Original) never learned the technique.

So, it’s not that Bulma "forgot" to tell Trunks. It’s that in Trunks' history, the teleportation never happened.



To be precise, there are 4 timelines, created by the interplay of two different Trunks and Cell's interference.
Timeline 1 (Original Future): Where Imperfect Cell comes from. Here, Trunks went to the past, got the Android blueprints, deactivated them, but was killed by Cell. (Goku didn't know IT here).
Timeline 2 (Unseen Past): The past visited by the Trunks from Timeline 1. No Cell Games happened here.
Timeline 3 (Main Series): Created when Cell arrived in Age 763. This triggered the butterfly effect (Goku learning IT).
Timeline 4 (Our Trunks' Future): Because our Trunks visited Timeline 3 (and trained in the Time Chamber), he returned strong enough to kill his Cell, creating a distinct future from Timeline 1.
The existence of Timeline 1 (where Cell comes from) is the smoking gun. In that history, no one had time-traveled to Age 763. Therefore, history played out 'naturally': Goku arrived by ship, fought physically, and left no teleportation data for the Spy Robot

[dbgtFO]

Yes, the Goku arrival time always rubbed me the wrong way thanks to everything you mention here.
Bulma should have given Trunks all the correct info, so it wouldn't make sense that she somehow neglected to tell him about Goku's teleportation, if that was how he came back and defeated Freeza and co. on Earth.

Only way would be if Toriyama was setting up this to be more conventional time travel, where Trunks was always the one to kill Freeza, so Bulma did not give him that info, so he could interfere on his own

You are confusing a "Time Loop" with the Multiverse Theory, which is how Dragon Ball actually works. There isn't just one future; there are at least 4 distinct timelines.

I wasn't confused or anything. I know fully well that it's multiverse and everything, I'm just saying that given the early parts of the plot not establishing that yet, Toriyama could have had time loop as an idea and therefore Trunks not knowing about teleportation.

[vilker]

Yes, the Goku arrival time always rubbed me the wrong way thanks to everything you mention here.
Bulma should have given Trunks all the correct info, so it wouldn't make sense that she somehow neglected to tell him about Goku's teleportation, if that was how he came back and defeated Freeza and co. on Earth.

Only way would be if Toriyama was setting up this to be more conventional time travel, where Trunks was always the one to kill Freeza, so Bulma did not give him that info, so he could interfere on his own

You are confusing a "Time Loop" with the Multiverse Theory, which is how Dragon Ball actually works. There isn't just one future; there are at least 4 distinct timelines.

I wasn't confused or anything. I know fully well that it's multiverse and everything, I'm just saying that given the early parts of the plot not establishing that yet, Toriyama could have had time loop as an idea and therefore Trunks not knowing about teleportation.

I see your point, but I honestly don't think Toriyama ever intended a bleak 'Time Loop' ending. Dragon Ball is a Shonen manga centered on breaking limits and defying destiny. Writing a story where the heroes struggle only to find out they are destined to fail (just like in the future) goes against the entire spirit of the series. Ending the manga with androids taking over the world seems completely illogical to me, given what Dragon Ball is all about.

If it were a closed loop, Trunks giving Goku the medicine to survive (when he is already dead in the future) wouldn't make sense; he is actively trying to break the course of history. Trunks also realizes later that saving this timeline won't fix his own future, which rules out the 'Back to the Future' logic.

Also, look at Trunks' reaction when he returns the second time: he immediately notices that everything has changed. He doesn't recognize Androids #19 and #20, and he comments that the Androids are stronger than the ones in his time.

It seems likely that Toriyama invented the 'Cell arriving earlier' plot point (the egg in Age 763) precisely to justify these inconsistencies, or that he already had another time travel scenario planned. It acts as the narrative cause: Cell's arrival was the extra variable that caused the timeline to diverge so much, leading to changes like the Androids being different (good guys) and, as my theory suggests, Goku learning Instant Transmission when he originally didn't.

[Zephyr]

Cell not knowing Teleportation is really all you even need to get this off the ground. My only issue with the larger theory you're sketching is that the Butterfly Effect, well, requires cause-and-effect to happen. When the cause and the effect are both on the same planet, it's very easy to see how the one could cause a domino chain leading to the other. But across planets, with no travel or interaction between them? How could Cell digging into the ground and incubating on Earth in any way causally impact what Goku does all the way on Yardrat? Sure, ki can be felt across space, but the big example of that is Perfect Cell being felt on Namek. Larval Cell probably wouldn't be a blip to someone on another planet.

[Saiya6Cit]

FGoku did use instant transmission to go with cyborg/mecha freezer. Trunks said it. He screw the timeline by killing freezer himself instead of waiting for Goku to show up because he had calculated he would not arrive on time, because Trunks did not know about Gokus ability to use instant transmission.

It has never been a question for me and this is how I understood it:

1.Cell knew the technique, he just chose not to use it earlier.

2.FGohan did not know how exactly it wws that Goku arrived to mecha/cyborg Freezer because they were too far away to realized, it was a large wasteland, most likely Goku showed up and when they turned their head to him, they assume he had quickly gotten out of a ship and flew. They were also probably shocked by Freezer and King’s cold humongous Ki as to realize of something that happened in a few seconds.

3. The ship was empty cause he got out of via instant transmission. It was still close to the area.

4. Yes, the future changed because of that difference, because Trunks arrived before Goku and killed freezer. Small changes eventually caused one of the FTrunks’ dead. I thought that was clear. It was the time line adjusting itself. As seen in many other scifi stories.

5. That was a result of pint 4 buddy.

[DanielSSJ]

I'm sorry, but there are too many other examples of Toriyama struggling with his own time travel rules for me to buy that this is an intentional example of the Butterfly Effect.

1. Forget Goku's teleportation, Cell wasn't even aware that Piccolo could regrow limbs until Piccolo did it in front of him, and his use of that ability and the 23rd Budokai and the fight against Raditz were way too early for that to be chalked up to time travel-related divergences.

2. Cell acts like Trunks was the one who killed Freeza and King Cold in his timeline when he explains the genetic material harvesting process, despite that obviously being impossible.

3. Trunks is concerned that if Bluma and Vegeta find out they're "supposed" to have him, he might never be born, and then begs Goku to keep it a secret, despite that not being how this brand of time travel works.

The Cell arc has a lot of oversights, this one isn't even a particularly big one.

[Mystic-han]

Or

Future Goku know teleporting and just used it to get rid of freeza and cold

Or

Freeza and cold fucked around long enough for him to arrive in the pod and end it

[vilker]

Cell not knowing Teleportation is really all you even need to get this off the ground. My only issue with the larger theory you're sketching is that the Butterfly Effect, well, requires cause-and-effect to happen. When the cause and the effect are both on the same planet, it's very easy to see how the one could cause a domino chain leading to the other. But across planets, with no travel or interaction between them? How could Cell digging into the ground and incubating on Earth in any way causally impact what Goku does all the way on Yardrat? Sure, ki can be felt across space, but the big example of that is Perfect Cell being felt on Namek. Larval Cell probably wouldn't be a blip to someone on another planet.

That is a very sharp observation. From a strictly physical perspective, you are right: a larva buried on Earth shouldn't physically impact Goku lightyears away.

However, I think we have to look at how Time Travel works in DB: it creates brand new timelines.
The moment Cell arrives in Age 763, the entire universe 'splits' into a new instance.

1st theory (best for me): Quantum Divergence: In fiction (and theory), when a new timeline is created, events aren't 'locked' to repeat exactly as the original unless acted upon. The new timeline introduces new variables (entropy). This new reality is random, it doesn't have to be repeated. In this new reality, Goku might have simply felt a whim to learn another technique, or a random variable shifted. The script was rewritten the moment the timeline split.

2nd theory: The 'Spirit' Factor: Remember that Goku was on Yardrat learning Spirit Control. The Yardratians are experts in manipulating spirit and space-time techniques (Instant Transmission). It is not a stretch to theorize that the arrival of a Time Machine—a massive violation of the natural order causing a rift in time—could be felt as a 'disturbance' by the Yardratian elders or a spiritually heightened Goku, even if they didn't know it was Cell.

So, the 'Butterfly Effect' here might not be Cell physically poking Goku, but the temporal rupture itself shifting the conditions of the universe slightly, leading Goku to master a move he originally skipped.

FGoku did use instant transmission to go with cyborg/mecha freezer. Trunks said it. He screw the timeline by killing freezer himself instead of waiting for Goku to show up because he had calculated he would not arrive on time, because Trunks did not know about Gokus ability to use instant transmission.

It has never been a question for me and this is how I understood it:

1.Cell knew the technique, he just chose not to use it earlier.

2.FGohan did not know how exactly it wws that Goku arrived to mecha/cyborg Freezer because they were too far away to realized, it was a large wasteland, most likely Goku showed up and when they turned their head to him, they assume he had quickly gotten out of a ship and flew. They were also probably shocked by Freezer and King’s cold humongous Ki as to realize of something that happened in a few seconds.

3. The ship was empty cause he got out of via instant transmission. It was still close to the area.

4. Yes, the future changed because of that difference, because Trunks arrived before Goku and killed freezer. Small changes eventually caused one of the FTrunks’ dead. I thought that was clear. It was the time line adjusting itself. As seen in many other scifi stories.

5. That was a result of pint 4 buddy.

Respectfully, point #1 and #2 rely heavily on headcanon that contradicts the actual manga dialogue.

1. Cell explicitly states he didn't know it. First time Cell is sourprised by Goku's IT.
You said: 'Cell knew the technique, he just chose not to use it earlier.'
This is incorrect. Upon returning as Super Perfect Cell, he explicitly explains his power-up: 'I was able to learn Goku's teleportation technique as well.'
He credits learning it to the self-destruction on King Kai's planet. If he had known it from the start (via Spy Robot data from Future Goku), he wouldn't say he just learned it, and he certainly wouldn't have been so desperate when Gohan was beating him into a corner. He would have used it to escape or tactical advantage. The fact he didn't have it proves the Spy Robot never recorded Future Goku using it.

2. The Gohan Factor.
It is impossible that Gohan 'didn't realize' for 3 years. Future Goku lived for years after killing Frieza before dying of the virus. Are you suggesting that in all those years of training together, Goku never mentioned: 'Hey guys, watch this, I can teleport'?
If Goku knew it, Gohan would know. If Gohan knew, he would have told Trunks. The fact Trunks is completely shocked by the technique in the Present proves Gohan never saw it.
Furthermore, Bulma and the other Z Fighters were there when Frieza arrived. They all would have sensed Goku's ki in milliseconds and asked him how he got there.

3. The 'Timeline Adjusting' vs Causality.
My theory isn't about magical timeline adjustments; it's about causality.
Fact: Robot records Frieza fight.
Fact: Cell has Robot's data.
Fact: Cell doesn't know IT.
Logical Conclusion: Robot didn't record IT. Therefore, Future Goku didn't use IT.

The empty ship is easily explained: Goku landed, walked out, and fought. Bulma recorded the landing time because that was the moment of arrival.
Bulma wouldn't have bothered to note the ship's coordinates; it's absurd if she hadn't even waited for it to land.
The fact that Bulma wrote down the day, time, and coordinates of the ship is crucial, as it's what saved them from being killed by Frieza. Their arrival in that ship was key to preventing Earth's destruction. The Z Fighters held out as best they could until Goku arrived; it's the only explanation.

4. Timeline changes
You are missing the chronology, buddy. That is exactly why Point 5 is crucial and distinct from Point 4.

If you say the divergence is caused by 'Trunks killing Frieza,' that happens in Age 764.

By Age 764, Goku is already in his spaceship returning to Earth. He has already finished his training on Yardrat.

Therefore, Trunks' arrival is too late to influence whether Goku learns Instant Transmission or not. The move is already learned (or not learned) by the time Trunks draws his sword.

This is why Cell's arrival in Age 763 is the key.

Cell arrives one year before Trunks and Frieza.

In Age 763, Goku is still on Yardrat.

This is the only event that happens early enough to butterfly-effect Goku's training schedule in outer space.

If the change was just Trunks (Age 764), Goku (and Cell) should have the same moveset in both timelines because his training was already done. The fact that his moveset is different proves the divergence started in 763 (Cell), not 764 (Trunks).


To finalize the theory, look at the empirical evidence presented by the characters themselves. It cannot be a coincidence.

There are only two characters in the entire series who originate from the Future Timeline:

Future Trunks

Imperfect Cell

And coincidentally, neither of them knows the technique.

The Verdict:
If it were just Trunks, you could argue 'maybe nobody told him'.
If it were just Cell, you could argue 'maybe the robot missed it'.
But when BOTH independent witnesses from the future —one biological and one mechanical— are completely unaware of the technique, the conclusion is undeniable: Future Goku never learned it.

Toriyama showed us through their reactions that the Future Timeline was fundamentally different in this aspect.

[vilker]

I'm sorry, but there are too many other examples of Toriyama struggling with his own time travel rules for me to buy that this is an intentional example of the Butterfly Effect.

1. Forget Goku's teleportation, Cell wasn't even aware that Piccolo could regrow limbs until Piccolo did it in front of him, and his use of that ability and the 23rd Budokai and the fight against Raditz were way too early for that to be chalked up to time travel-related divergences.

2. Cell acts like Trunks was the one who killed Freeza and King Cold in his timeline when he explains the genetic material harvesting process, despite that obviously being impossible.

3. Trunks is concerned that if Bluma and Vegeta find out they're "supposed" to have him, he might never be born, and then begs Goku to keep it a secret, despite that not being how this brand of time travel works.

The Cell arc has a lot of oversights, this one isn't even a particularly big one.

1. About Piccolo
Your claim is that Cell 'wasn't aware Piccolo could regrow limbs.' That is false. Cell possesses Piccolo's cells (harvested from the Saiyan Saga). Biologically, Cell knows regeneration is possible. He was simply outsmarted by Piccolo's bluff, he wasn't ignorant of the ability itself. It was arrogance, not a plot hole. It was a way to explain to the viewer the origin of Cell.

2. About Spy Robot
The Spy Robot explicitly states in the manga that it collected cells from Frieza and King Cold, and then stopped collecting data because it had enough. Cell never claims Trunks killed Frieza in his original timeline; the robot data simply confirms Frieza died and then stop to collect data about Trunks fighting androids.
Cell mentions Trunks because he killed him; in fact, Cell is surprised when he sees Trunks in that same timeline and then realizes that he also traveled with the time machine. Toriyama is aware of the events; it's just somewhat confusing that he didn't collect any of Trunks' cells, but he's referring to the Trunks who fights the androids.

Just as Cell has data from Frieza and his father because the robot saw the fight against Goku, he should have the cells of the shunkanido, but that's not the case, because that Goku arrived in the spaceship and didn't use IT.

3. About Trunks fears
You are interpreting his fear as a paradox, but look at it from his perspective: He isn't necessarily afraid of fading away (Grandfather Paradox); he is afraid that if Vegeta and Bulma know too much, they might change their behavior and never conceive the Trunks of this timeline. Trunks wants to ensure his alternate self is born. That is a valid concern about causality, not a misunderstanding of time travel rules.



But here is the key difference:
Even if we accept those as minor oversights, the Instant Transmission issue is structural.
It relies on Cause and Effect via the Spy Robot.

If Goku used IT -> Robot records it -> Cell has it.

Cell doesn't have it.

Therefore, the Robot didn't see it.

This isn't a character making a wrong guess (like Trunks) or acting (like Cell). It is a hard-drive data discrepancy. The only logical explanation for the empty data slot is that the event (teleportation) never happened in the timeline where Cell came from.

[vilker]

Or

Future Goku know teleporting and just used it to get rid of freeza and cold

Or

Freeza and cold fucked around long enough for him to arrive in the pod and end it

Your first option is mathematically impossible according to the manga.

Option 1: 'Future Goku knew teleporting and used it.'

The Flaw: Dr. Gero's Spy Robot was watching that fight to collect data for Cell.

The Proof: If Goku had used Instant Transmission against Frieza, the Robot would have recorded that data. Consequently, Cell would have been born knowing the technique (just like he knows the Kamehameha).

The Reality: Imperfect Cell does not know Instant Transmission. He explicitly states he learned it after self-destructing in the Present timeline.

Conclusion: Since Cell didn't have the data, Future Goku never used the move.

Option 2: 'Arrive in the pod.'

This is exactly my point! He arrived in the pod because he had to. If he knew Instant Transmission, he wouldn't have risked waiting in the pod while Frieza threatened the Earth. He would have teleported instantly. The fact that he stayed in the pod confirms he didn't know the technique.

[PhantomSaiyan]

It makes no sense for Future Goku to not learn IT.

How would Trunks going back in time influence what Goku learns on Yardrat? Besides, Goku used IT to teleport to Freeza and Cold. Thread solved.

As for your Cell point, that's just Toriyama not being the type of writer that remembers the details well. Stop trying to headcanon Toriyama's mistakes as something else, it's just that, a mistake.

Because again, it makes absolutely zero sense for Trunks' time travel to somehow change what technique Goku learned on Yardrat, it's absolutely ridiculous.

[vilker]

It makes no sense for Future Goku to not learn IT.

How would Trunks going back in time influence what Goku learns on Yardrat? Besides, Goku used IT to teleport to Freeza and Cold. Thread solved.

As for your Cell point, that's just Toriyama not being the type of writer that remembers the details well. Stop trying to headcanon Toriyama's mistakes as something else, it's just that, a mistake.

Because again, it makes absolutely zero sense for Trunks' time travel to somehow change what technique Goku learned on Yardrat, it's absolutely ridiculous.

You are misunderstanding the timeline mechanics and dismissing hard evidence as 'mistakes' just because it challenges the standard view.

1. It wasn't Trunks. It was Cell.
You asked: 'How would Trunks going back in time influence what Goku learns on Yardrat?'
You are right, Trunks (arriving in Age 764) couldn't change it because Goku was already done training.
BUT you are forgetting Cell.
Cell arrived in his Time Machine in Age 763.
This is one full year before Trunks arrives.
In Age 763, Goku is still in space on Yardrat.
The arrival of a time traveler (Cell) in 763 is the event that causes the 'Butterfly Effect' ripple that reaches Goku in space, not Trunks' arrival in 764.

2. It's not a 'mistake' if the plot relies on it.
Calling it a 'Toriyama mistake' is the lazy way out.
If it were just Trunks not knowing, maybe. But we have Imperfect Cell.

The Logic Chain: If Future Goku used IT -> Spy Robot records it -> Cell is born with IT.
The Reality: Cell explicitly states he doesn't know IT until he self-destructs in the Present.
The Conclusion: Since Cell (the ultimate biological database) didn't have the data, the event (Future Goku using IT) never happened.

Why would I accept it as a 'mistake' when the manga forces this fact twice with TWO different characters from the future?

-Trunks doesn't know it.
-Cell doesn't know it (despite having spy data).

That is not a mistake; that is a consistent narrative showing that the Future Timeline played out differently.




Trunks admitted it himself: History changed too much, way beyond just his interference. But you have to look at the dates to see who caused what.

1. Divergences caused by Cell (Arrival in Age 763 - The "Root" Cause)
Since Cell arrived one year before Trunks, his presence (The Butterfly Effect) altered events while Goku was still in space and Gero was still working.

-Goku: Alters his path on Yardrat -> Learns Instant Transmission.
-The Virus: Butterfly effect shifts the timing -> Goku gets sick later.
-The Androids: Gero's plans shift slightly -> #19 and #20 appear first; #17 and #18 become stronger but less aggressive; #16 appears.

2. Divergences caused by Trunks (Arrival in Age 764)
Trunks arrived later, so his impact is only on immediate events.
-Frieza: Killed by sword instead of Goku.
-Survival: Goku physically receives the medicine.

The Conclusion:
You can't blame Trunks for the Instant Transmission because he arrived in 764, when Goku was already done training.
The only variable present in 763 (during Goku's training) was Cell.
Therefore, Cell is the reason Goku learned the move. It fits the timeline perfectly.

[PhantomSaiyan]

You are misunderstanding the timeline mechanics and dismissing hard evidence as 'mistakes' just because it challenges the standard view.


The Conclusion:
You can't blame Trunks for the Instant Transmission because he arrived in 764, when Goku was already done training.
The only variable present in 763 (during Goku's training) was Cell.
Therefore, Cell is the reason Goku learned the move. It fits the timeline perfectly.

On one hand, I respect your dedication to explaining plotholes with in universe reasons that somewhat make sense (I still don't see how Cell going back to the past would make Goku not learn IT, but I can cut you some amount of slack on it because Trunks going back to the past somehow made 17 and 18 not as evil, and stronger, so eh)

But on the other hand, as much as you can explain it away, it's clear that Toriyama didn't think about this whatsoever. This is the same guy that came up with Cell's nucleaus after he already drew him with his whole upper body destroyed, clearly he did not come up to your same conclusion, you have to admit that at least.

He is notorious for writing week to week without much of a plan and creating tons of mistakes and inconsistencies as a result, so just because you can come up with something that fits, it does not mean that it was created with that in mind.

His writing style also doesn't leave anything unsaid. If there's information that we the readers should know, then he ALWAYS without exception makes a character do exposition on it (he basically speaks through his characters). If a character doesn't talk about it, then it likely wasn't in Toriyama's head.

A for effort though, I didn't mean to be dismissive
I could adopt your theory as a headcanon of mine no problem, I have no issues with things that "challenge the standard view, I just know how Toriyama writes that's all, so I can't in a million years convince myself that he thought about all of this while writing.

[vilker]

You are misunderstanding the timeline mechanics and dismissing hard evidence as 'mistakes' just because it challenges the standard view.


The Conclusion:
You can't blame Trunks for the Instant Transmission because he arrived in 764, when Goku was already done training.
The only variable present in 763 (during Goku's training) was Cell.
Therefore, Cell is the reason Goku learned the move. It fits the timeline perfectly.

On one hand, I respect your dedication to explaining plotholes with in universe reasons that somewhat make sense (I still don't see how Cell going back to the past would make Goku not learn IT, but I can cut you some amount of slack on it because Trunks going back to the past somehow made 17 and 18 not as evil, and stronger, so eh)

But on the other hand, as much as you can explain it away, it's clear that Toriyama didn't think about this whatsoever. This is the same guy that came up with Cell's nucleaus after he already drew him with his whole upper body destroyed, clearly he did not come up to your same conclusion, you have to admit that at least.

He is notorious for writing week to week without much of a plan and creating tons of mistakes and inconsistencies as a result, so just because you can come up with something that fits, it does not mean that it was created with that in mind.

His writing style also doesn't leave anything unsaid. If there's information that we the readers should know, then he ALWAYS without exception makes a character do exposition on it (he basically speaks through his characters). If a character doesn't talk about it, then it likely wasn't in Toriyama's head.

A for effort though, I didn't mean to be dismissive
I could adopt your theory as a headcanon of mine no problem, I have no issues with things that "challenge the standard view, I just know how Toriyama writes that's all, so I can't in a million years convince myself that he thought about all of this while writing.

I appreciate the honesty and the 'A for effort'! I get where you are coming from. We all know Toriyama wrote by the seat of his pants (the Cell nucleus is a classic blunder).

But I think you are falling into a trap: Just because Toriyama improvised doesn't mean he didn't fix his own plot holes using Retcons.

1. Toriyama wasn't working alone.
You say Toriyama 'forgot' details. Remember, he had a team of editors (like Yu Kondo during this arc) guiding him. If there was a massive contradiction, they usually pointed it out (like when they told him to change #19 and #20, and then #17 and #18). It is highly unlikely that no one on his team noticed that Trunks didn't know the technique if Goku was supposed to know it. The fact that it stayed in the manga suggests it was intentional.

2. Cell's existence mandates a Double Split.
The mere appearance of Cell confirms that the timelines bifurcated twice, not once.

First Split: Trunks creates the 'Unseen Past'.
Second Split: Cell kills a Trunks, steals the machine, and travels to Age 763, creating our timeline.

This implies that a Future Trunks died at Cell's hands in the original timeline. The story acknowledges this dark reality. If the story is complex enough to kill off a main character in an alternate timeline, it is complex enough to have 'Butterfly Effects' like the Instant Transmission change.
You can't have a 'Dead Trunks' timeline and a 'Living Trunks' timeline without accepting that history played out differently in each.

3. 'Show, Don't Tell'.
You claim Toriyama always uses exposition. I disagree. He was also a master of visual storytelling.
He didn't need a character to say: 'Future Goku didn't know IT.'
He showed us Trunks (Goku's student's pupil) being totally bewildered by the move.
He showed us Cell (the spy computer) not knowing the move.
Attributing everything to 'Toriyama just forgot' is doing a disservice to the story. The dates (763 vs 764) and the dead Trunks plotline are too specific to be mistakes.

Give the manga a re-read with this perspective; you might find that what looked like 'mistakes' were actually clues left by the Time Travel plot.




All people usually are focusing too much on 'Physical Causality' (Domino Effect) and ignoring 'Quantum Divergence' (Entropy).

In time travel mechanics involving Multiverse theory (like DBZ), creating a new timeline isn't just inserting a character; it is duplicating the entire universe.
When a timeline splits, reality is 're-rolled'. Variables that depend on chance, biology, or psychology are subject to new outcomes even without direct interference.

Think of it as reloading a save file in a corrupt video game. Even if you stand still, the RNG (Random Number Generator) might produce different enemy spawns.

Proof that DBZ works on Quantum Chance, not just Contact:

The Heart Virus (Biological RNG):
Trunks didn't touch Goku's heart cells. Yet, in the Future, the virus attacked Goku immediately after Frieza. In the Present, it attacked 3 years later.

Why? Trunks didn't delay the virus. The virus simply mutated differently in this new timeline due to biological probability. The timeline split 're-rolled' the virus's incubation period.

Dr. Gero's Whim (Psychological RNG):
Trunks never met Gero. Yet, in the Future, Gero released #17 and #18. In the Present, Gero decided to build #19 and convert himself into #20 first.

Why? Trunks didn't convince him. Gero simply made a different arbitrary choice that morning. In a new timeline, neurons fire differently.

Conclusion:
If a virus can delay itself by 3 years and a scientist can change his entire project roadmap without any direct contact from Trunks, then Goku is subject to the same rule.

In Timeline 1: The 'coin flip' of destiny made Goku decide to take the ship.

In Timeline 3 (Cell's arrival): The timeline split caused a microscopic shift in probability. Goku felt a whim to train a bit longer, or the Yardratians insisted more.

It is not magic. It is the butterfly effect at a quantum level. The moment Cell arrived in Age 763, the atoms of the universe were copied, and the events played out with slight variations.

[PhantomSaiyan]

I appreciate the honesty and the 'A for effort'! I get where you are coming from. We all know Toriyama wrote by the seat of his pants (the Cell nucleus is a classic blunder).

But I think you are falling into a trap: Just because Toriyama improvised doesn't mean he didn't fix his own plot holes using Retcons.

Give the manga a re-read with this perspective; you might find that what looked like 'mistakes' were actually clues left by the Time Travel plot.

Well, I'll concede that what I said about Toriyama is just my assumption based on what I've read of him from interviews and such, so I can't claim to know 100% his intent when writing, so you might as well be right about this.

But yeah all in all, interesting arguments, I don't mind using this as a new interpretation of the events whenever I'll re read the manga, I'll definitely keep it in mind, thanks for the post

[DanielSSJ]

1. About Piccolo
Your claim is that Cell 'wasn't aware Piccolo could regrow limbs.' That is false. Cell possesses Piccolo's cells (harvested from the Saiyan Saga). Biologically, Cell knows regeneration is possible. He was simply outsmarted by Piccolo's bluff, he wasn't ignorant of the ability itself. It was arrogance, not a plot hole. It was a way to explain to the viewer the origin of Cell.

Piccolo directly calls Cell out for not knowing that he can regrow limbs in spite of inheriting his blood. The dialogue directly indicates Cell was ignorant of it.

Spoiler:

2. About Spy Robot
The Spy Robot explicitly states in the manga that it collected cells from Frieza and King Cold, and then stopped collecting data because it had enough. Cell never claims Trunks killed Frieza in his original timeline; the robot data simply confirms Frieza died and then stop to collect data about Trunks fighting androids.
Cell mentions Trunks because he killed him; in fact, Cell is surprised when he sees Trunks in that same timeline and then realizes that he also traveled with the time machine. Toriyama is aware of the events; it's just somewhat confusing that he didn't collect any of Trunks' cells, but he's referring to the Trunks who fights the androids.

Just as Cell has data from Frieza and his father because the robot saw the fight against Goku, he should have the cells of the shunkanido, but that's not the case, because that Goku arrived in the spaceship and didn't use IT.

Again, the dialogue does not really support this. In that scene, Cell is talking about himself, not the other, fetal version of him that exists in this timeline. "We could've taken the cells of that Trunks guy as well, but there was already enough from the Saiyans." Actually, considering this Cell has only recently hatched from his egg after lying dormant for three years and immediately attacked Ginger Town, there's no reason at all for him to be so sure that Trunks' cells weren't harvested. Everything he knows, he says he's been told by Gero's computer, but he couldn't have visited Gero's basement laboratory in this timeline to find out what's been going on. So yes, he is talking about it like Gero's computer in his timeline had the opportunity to harvest Trunks' cells in his time and chose not to. It's a mistake on Toriyama's part.

3. About Trunks fears
You are interpreting his fear as a paradox, but look at it from his perspective: He isn't necessarily afraid of fading away (Grandfather Paradox); he is afraid that if Vegeta and Bulma know too much, they might change their behavior and never conceive the Trunks of this timeline. Trunks wants to ensure his alternate self is born. That is a valid concern about causality, not a misunderstanding of time travel rules.

There's actually another example of Trunks not quite understanding the rules of time travel. At one point, he offers to go back in time to destroy #17 and #18 before they're activated, and it isn't until Gohan asks what will happen to the Androids in the present that Trunks remembers that changing the past won't change anything in this timeline, something he should've already known before he made the suggestion.

Spoiler:

But here is the key difference:
Even if we accept those as minor oversights, the Instant Transmission issue is structural.
It relies on Cause and Effect via the Spy Robot.

If Goku used IT -> Robot records it -> Cell has it.

Cell doesn't have it.

Therefore, the Robot didn't see it.

This isn't a character making a wrong guess (like Trunks) or acting (like Cell). It is a hard-drive data discrepancy. The only logical explanation for the empty data slot is that the event (teleportation) never happened in the timeline where Cell came from.

I mean, if you really need a rational explanation that isn't "Toriyama fucked up", you could just say that maybe there was a malfunction in Gero's computer in the 24 years it had been running uninterrupted, and that some of its data had been lost or corrupted.

Other than that, Trunks not hearing about Goku's teleportation skill is pretty easy to account for. Who knows what stories Bluma or Gohan decided to tell Trunks growing up, parents don't tend to explain their entire life story to their kids. Bluma telling him the precise time and coordinates of when Goku's ship arrived, but neglecting to say that Goku arrived much sooner because he teleported his harder to square, but it could've just slipped her mind. Those memories where twenty years old for her, and it's not like Bluma's not a bit of a scatterbrain. Not exactly ideal, but easier than explaining how Cell's time travel caused Goku to learn a move in the year and change he spent in space in one timeline but not the other, or how the Earth was still standing if Goku was hours late to the fight in Trunks and Cell's timelines.

[vilker]

1. About Piccolo
Your claim is that Cell 'wasn't aware Piccolo could regrow limbs.' That is false. Cell possesses Piccolo's cells (harvested from the Saiyan Saga). Biologically, Cell knows regeneration is possible. He was simply outsmarted by Piccolo's bluff, he wasn't ignorant of the ability itself. It was arrogance, not a plot hole. It was a way to explain to the viewer the origin of Cell.

Piccolo directly calls Cell out for not knowing that he can regrow limbs in spite of inheriting his blood. The dialogue directly indicates Cell was ignorant of it.

Spoiler:

Wait a second. You are basing your entire argument on an anime screenshot with an English dub/sub translation.
In a serious lore discussion, the original Japanese Manga is the only valid canon. The anime adds filler and changes dialogue constantly.

1. Context of the 'Idiot' remark:
Even if we accept the scene, Piccolo calling him an 'idiot' doesn't necessarily mean Cell didn't know regeneration existed in his DNA. It implies Cell was careless.
It’s like the Solar Flare (Taiyoken) example:

Everyone knows the Solar Flare exists.

Yet, when Cell used it to escape, everyone was caught off guard and blinded.

Does that mean they 'didn't know' the technique? No. It means they didn't expect him to use it strategically at that moment.

2. Tactical Oversight vs. Ignorance:
Cell was arrogant. He thought he had Piccolo completely beaten. He didn't 'realize' Piccolo could regenerate in that specific context because he assumed Piccolo was genuinely damaged and desperate. He underestimated his opponent's strategy, not his own biology.

3. The Core Issue remains:
Regardless of the regeneration debate (which is biological/passive), Instant Transmission is an active technique.
If the Spy Robot recorded the Frieza fight, it recorded the moves.

If Goku used IT -> Robot records IT -> Cell knows IT.

Cell doesn't know IT.

Therefore, the Robot didn't see IT.

Please, let's stick to the Manga logic, not anime screenshots.

2. About Spy Robot
The Spy Robot explicitly states in the manga that it collected cells from Frieza and King Cold, and then stopped collecting data because it had enough. Cell never claims Trunks killed Frieza in his original timeline; the robot data simply confirms Frieza died and then stop to collect data about Trunks fighting androids.
Cell mentions Trunks because he killed him; in fact, Cell is surprised when he sees Trunks in that same timeline and then realizes that he also traveled with the time machine. Toriyama is aware of the events; it's just somewhat confusing that he didn't collect any of Trunks' cells, but he's referring to the Trunks who fights the androids.

Just as Cell has data from Frieza and his father because the robot saw the fight against Goku, he should have the cells of the shunkanido, but that's not the case, because that Goku arrived in the spaceship and didn't use IT.

Again, the dialogue does not really support this. In that scene, Cell is talking about himself, not the other, fetal version of him that exists in this timeline. "We could've taken the cells of that Trunks guy as well, but there was already enough from the Saiyans." Actually, considering this Cell has only recently hatched from his egg after lying dormant for three years and immediately attacked Ginger Town, there's no reason at all for him to be so sure that Trunks' cells weren't harvested. Everything he knows, he says he's been told by Gero's computer, but he couldn't have visited Gero's basement laboratory in this timeline to find out what's been going on. So yes, he is talking about it like Gero's computer in his timeline had the opportunity to harvest Trunks' cells in his time and chose not to. It's a mistake on Toriyama's part.

You are assuming the Spy Robot stopped watching immediately after Frieza died. That is incorrect.

1. The Robot watched for years.
In Cell's original timeline (Timeline 1), the Spy Robot didn't just vanish. It continued gathering data for the supercomputer to create Cell.

Did Trunks exist in Timeline 1? Yes. He grew up and fought the Androids for years.

Did the Robot see him? Absolutely. The robot observed Future Trunks fighting #17 and #18.

The Decision: The computer analyzed this Future Trunks and decided: 'We already have enough Saiyan DNA from Goku and Vegeta. We don't need this kid.'

So when Cell says "We could've taken the cells of that Trunks guy as well," he isn't referring to the Frieza fight specifically. He is referring to the decades of data the computer had on the Z-Fighters in his timeline. It's not a plot hole; it's the robot rejecting Trunks' data later in the timeline.

2. Cell's Knowledge.
Cell doesn't need to visit the basement to know what he is made of. He is the biological result. He knows instinctively that he has Frieza's cells but lacks Trunks'.

3. Back to the Main Point (The Anchor).
Regardless of when it analyzed Trunks, we know for a fact the Robot collected data during the Frieza invasion (because Cell has Frieza and Cold's cells).

In Timeline 1, Goku fought Frieza.

The Robot recorded that fight.

If Goku had used Instant Transmission, the Robot would have recorded it as a technique.

Cell does not know the technique.

Therefore, Future Goku defeated Frieza without it. The logic holds up.

3. About Trunks fears
You are interpreting his fear as a paradox, but look at it from his perspective: He isn't necessarily afraid of fading away (Grandfather Paradox); he is afraid that if Vegeta and Bulma know too much, they might change their behavior and never conceive the Trunks of this timeline. Trunks wants to ensure his alternate self is born. That is a valid concern about causality, not a misunderstanding of time travel rules.

There's actually another example of Trunks not quite understanding the rules of time travel. At one point, he offers to go back in time to destroy #17 and #18 before they're activated, and it isn't until Gohan asks what will happen to the Androids in the present that Trunks remembers that changing the past won't change anything in this timeline, something he should've already known before he made the suggestion.

Spoiler:

You are right about that scene being in the manga. I admit that was a momentary lapse by Trunks (likely used by Toriyama as a narrative device to re-explain the timeline rules to the audience).

However, that does not invalidate the theory.

Trunks' motivations were always consistent with the facts:

The Hope in Goku: He wanted to change the past to save Goku because Bulma told him Goku would find a way to win. (And she was right—Goku found the path to Ascended Saiyan/Time Chamber).

The Strategy: His objective was to find a clue to defeat the Androids or, ultimately, bring Goku to the future to eliminate them.

The Outcome: Since Trunks became strong enough himself, he no longer needed to bring anyone back. He solved his own problem.

Regarding his attachment to this timeline:
This has nothing to do with him 'not caring' about this specific timeline. He cares deeply.
Proof: When Dr. Gero attacked Bulma's plane, Trunks was the first and only one to panic and rush to save his mother and his baby self, while Vegeta stood there watching. He explicitly wants to save his family in this timeline too, regardless of the multiverse rules.

So, Trunks having a 'brain fart' about the rules due to stress doesn't change the physical reality of the Spy Robot data or Cell's design.

But here is the key difference:
Even if we accept those as minor oversights, the Instant Transmission issue is structural.
It relies on Cause and Effect via the Spy Robot.

If Goku used IT -> Robot records it -> Cell has it.

Cell doesn't have it.

Therefore, the Robot didn't see it.

This isn't a character making a wrong guess (like Trunks) or acting (like Cell). It is a hard-drive data discrepancy. The only logical explanation for the empty data slot is that the event (teleportation) never happened in the timeline where Cell came from.

I mean, if you really need a rational explanation that isn't "Toriyama fucked up", you could just say that maybe there was a malfunction in Gero's computer in the 24 years it had been running uninterrupted, and that some of its data had been lost or corrupted.

Other than that, Trunks not hearing about Goku's teleportation skill is pretty easy to account for. Who knows what stories Bluma or Gohan decided to tell Trunks growing up, parents don't tend to explain their entire life story to their kids. Bluma telling him the precise time and coordinates of when Goku's ship arrived, but neglecting to say that Goku arrived much sooner because he teleported his harder to square, but it could've just slipped her mind. Those memories where twenty years old for her, and it's not like Bluma's not a bit of a scatterbrain. Not exactly ideal, but easier than explaining how Cell's time travel caused Goku to learn a move in the year and change he spent in space in one timeline but not the other, or how the Earth was still standing if Goku was hours late to the fight in Trunks and Cell's timelines.

You are suggesting that the explanation relies on a massive chain of convenient accidents: a magical computer glitch + Bulma losing her memory + Gohan never speaking up.
But you are overlooking the statistical impossibility of your claim and the deliberate narrative choices by Toriyama.

1. The 'Computer Glitch' Fallacy (Statistical Impossibility)
You suggest Gero's computer might have 'malfunctioned' and lost data.

The Reality: Cell is a biological masterpiece. He knows the Kamehameha, Solar Flare, Special Beam Cannon, Death Beam, and even the logic of the Spirit Bomb.

The Odds: What are the odds that a random computer malfunction would delete only and exclusively the single most useful combat technique (Instant Transmission) while keeping every other move from the Saiyan and Frieza Sagas perfectly intact?
That is not a 'malfunction'; that is selective convenience to fit your narrative. If the computer were corrupted, Cell would have missing patches of memory or genetic defects. He doesn't. He is perfect, minus that one specific move.

2. The 'Bulma was there' Factor
You called Bulma a 'scatterbrain'. We are talking about the woman who built a Time Machine in a post-apocalyptic bunker. She deals in hard data, not vague memories.

The Logic: Bulma wasn't just hearing a story 20 years later; she was physically present at the landing site. If Goku had teleported out of thin air 3 hours early, why on earth would she record the ship's coordinates as the arrival point? The ship would be irrelevant.

The Witnesses: Vegeta, Piccolo, Gohan... they were all there. If Goku suddenly materialized (IT) instead of walking out of the ship, everyone would have been shocked.

The Proof: The fact that the future history books record the ship's landing as the moment of return proves he arrived via the ship.

3. 'Why didn't Frieza destroy Earth?':
Simple: Frieza's Arrogance.
Frieza didn't come to blow up Earth from space (he could have done that instantly). He came to kill Goku personally. He sensed Goku's ship approaching. He would absolutely wait 3 hours just to have the satisfaction of killing the Super Saiyan with his own hands. The Z-Fighters likely fought a desperate stalling battle against his soldiers (which explains why they were all dead or traumatized in the future).

4. The 'Egg Plot' is the Smoking Gun
This prevents this from being a simple 'mistake'. Let's assume for a second that you are right: that everyone forgot, the computer glitched, and Goku kept secrets.
Then why did Toriyama write such a deeply convoluted backstory for Cell?

If Toriyama just wanted a villain to show up, he could have simply let Cell arrive in Age 767 in his Imperfect Form, stepping out of the machine ready to fight. Simple, clean, no plot holes.
Instead, Toriyama went out of his way to complicate the script:

-Cell had to revert to an Egg.
-He had to travel back to Age 763 (not 767).
-He had to bury himself underground for 4 years.
-Kami mysteriously felt a disturbance for years.
-Bulma suddenly gets a photo of an old time machine.

Why invent this 'he didn't fit in the machine' excuse?
Why force a villain to be buried for 4 years if he could just arrive 'now'?
Because Toriyama needed a timeline divergence to happen years before Trunks arrived. He needed a root cause for the 'Butterfly Effect'.
The fact that he went out of his way to place Cell in Age 763 (while Goku was in space) proves that the timeline changes (including Goku's training) were intentional results of that early arrival.

In fact, Cell explicitly states: 'The time machine was already set for Age 763... I just had to push the button.'

This implies that the original plan was for Trunks to travel to Age 767 (after the Androids appeared) to announce that he had stopped them using the shutdown remote built by Bulma from Dr. Gero's blueprints.

If Cell didn't change the date, that means Future Trunks had set it to Age 763.
But why? It makes absolutely zero tactical sense for Trunks to travel to Age 763.

In 763, Frieza hasn't arrived yet.
Goku is still in space.
The Androids are years away.
Trunks' target was always 764 (Frieza) or 767 (Androids). Going to 763 serves no purpose for him.

The 'Toriyama Patch':
Since there is no logical reason for Trunks to choose that date, the date Age 763 exists solely because Toriyama needed it to exist.
He forced the machine to land in 763—defying Trunks' character logic—because he needed the timeline to diverge specifically at that point.

Why 763? Because it is the only window of time where Goku is still training on Yardrat.

By forcing the machine to 763 (via a plot device that makes no sense for Trunks), Toriyama ensures that Cell's arrival creates the Butterfly Effect that alters Goku's training path.

The fact that the machine was 'magically' set to the exact year needed to alter Goku's training (Age 763), despite it making no sense for Trunks to go there, proves that Toriyama deliberately engineered the date to fix the plot holes (like the Instant Transmission).

Conclusion:
Your explanation requires: A magical computer glitch + Bulma losing her memory + Gohan never mentioning his dad's best move + Toriyama writing a complex backstory for absolutely no reason.
My explanation requires: One Single Divergence Point (Cell) that alters the timeline naturally.
My theory respects the characters' intelligence, the robot's efficiency, and the author's narrative choices. Yours insults them.

[DanielSSJ]

Not going to address all of this, but:

1. There isn't a perfect translation of the manga available (Viz is noticably imperfect), and I can't read Japanese. Steve Simmons' subtitles are generally accepted as the best official translation Dragon Ball's ever relieved, and Piccolo's dialogue matched up well enough to the only translation of the manga available to me ["But how could you not know about my powers of regeneration? You have my cells."], so I figured it was probably correct.

2. Regarding the computer, regardless of how much of a genius Gero is, his computer was left alone in a cave for over 20 years. If it got a little humid, or if there were a power surge or outage, or an earthquake, yeah, something could've been lost.

3. Yes, Bluma is a scatterbrain. She's an engineering genius, but she's also prone to lapses in common sense, like when she accidentally blew up Nappa's spaceship in the previous arc. So yeah, I could easily imagine a scene of Future Bluma watching Trunks disappear and then immediately going "Shit, Goku got there early because he teleported in, didn't he?"

4. The whole point of this post was that there's no logical, in-universe answer for Cell not knowing that Goku could teleport, and your ultimate answer is that Future Trunks B selected a different, earlier year to return to the past for no logical, in-universe reason.

They're all just oversights. The Cell arc is the most ambitiously complex plot Toriyama's ever attempted in Dragon Ball, and he struggles to execute it. This isn't even a dig at Toriyama. Time travel plots are hard to get right when you have ample time to fine-tune them, and Toriyama was having to come up with the story every week, with former and current editors requesting changes to the plot as he's writing it. So yeah, I do think Cell and Trunks not knowing about Goku's teleportation is just an oops with no in-universe explanation.