Can Anyone Give Me Some Clarification on Cell?

[Xyex]

The easiest answered is that #17 or #18 killed him. We know he was weakened from his larval stage, and that even after absorbing a town (or more?) he was weaker than Piccolo, who was on-par with #17. Even more simply - Cell went around absorbing people, the only reason he would do so is if he wasn't powerful enough to absorb #17 and #18.

Further, assuming #16 was activated, he was even stronger than Cell after absorbing enough people to satisfy himself.

Except Cell would have gone around absorbing people until he was strong enough to take on Piccolo/17/18 as he did in the series. He would have fought 17 and absorbed him and thus the timeline Trunks-B comes from is voided.

Trunks presence seems to really have only affected:
1) Goku surviving the Heart Virus.
2) 16 being activated (since the Z Fighters were able to chase Gero to his lab and cause a ruckus thre).
3) Changes fuled by Goku's continued presence (Such as RoSaT training and Piccolo and Tien not being killed by Semi-Perfect Cell).

In a timeline without Trunks 16 likely wouldn't be activated (Gero would have had more time to prepare for the release of 17 and 18), Cell would absorb people as normal until and following encountering the Piccolo/Kami fusion (assuming he isn't killed when he locates the Androids), and so on until we get to the Imperfect Cell VS. 17 encounter. There 16 wouldn't be around to pose a threat and Cell would absorb 17 without issue. If 16 were there things wouldn't change (Trunks is a non-factor in this encounter).

So now we've got Semi-Perfect Cell running around, and likely no Z Fighters left. And in a few minutes he'd catch 18 and Perfect Cell would emerge and the Androids would be gone. This is definitely not the timeline that Trunks is from.

[desirecampbell]

If you're assuming that Trunks' visit to the past caused #16 to be activated, then we could just as easily say that Cell never came out of the ground. If that's all it takes to explain why a character did or didn't show up...

[Onikage725]

If you're assuming that Trunks' visit to the past caused #16 to be activated, then we could just as easily say that Cell never came out of the ground. If that's all it takes to explain why a character did or didn't show up...

But it probably is why 16 was activated. He is constantly admonishing himself in the series for having altered events. By revealing himself as another powerful opponent, he likely panicked Gero. 17 and 18 thus wound up being both more powerful and more stable (not that it did a lick of good for Gero, but they did lack the crazed bloodlust of their future selves). It also lead to him being more afraid of them, and shelving them in favor of models 19 and 20. He appears first, the Z Senshi, warned by Trunks, kick his ass, etc etc. All of these changes occur after Trunks' visit, and Trunks attributes them to his having fucked with the timeline.

[desirecampbell]

But it probably is why 16 was activated. He is constantly admonishing himself in the series for having altered events. By revealing himself as another powerful opponent, he likely panicked Gero. 17 and 18 thus wound up being both more powerful and more stable (not that it did a lick of good for Gero, but they did lack the crazed bloodlust of their future selves). It also lead to him being more afraid of them, and shelving them in favor of models 19 and 20. He appears first, the Z Senshi, warned by Trunks, kick his ass, etc etc. All of these changes occur after Trunks' visit, and Trunks attributes them to his having fucked with the timeline.

Huh? None of that explains why #16 wouldn't have been activated.

Do you mean that Gero saw Trunks defeat Freeza and then decided that he should keep the 'failed' #16 "just in case"? That can't be it, because we get it straight from Gero that Trunks' initial appearance was seen but judged inconsequential.

Do you mean Trunks' second appearance, confronting Gero and #19 caused him to activate #16? Two problems there, first Trunks was just one of three possible Super Saiyans at that point, plus Piccolo - any of them should have scared Gero enough to go for back-up (which he did); second, Gero activates #17 and #18, he refuses to activate #16.


Or have I missed something?

[Onikage725]

Huh? None of that explains why #16 wouldn't have been activated.

Do you mean that Gero saw Trunks defeat Freeza and then decided that he should keep the 'failed' #16 "just in case"? That can't be it, because we get it straight from Gero that Trunks' initial appearance was seen but judged inconsequential.

Do you mean Trunks' second appearance, confronting Gero and #19 caused him to activate #16? Two problems there, first Trunks was just one of three possible Super Saiyans at that point, plus Piccolo - any of them should have scared Gero enough to go for back-up (which he did); second, Gero activates #17 and #18, he refuses to activate #16.


Or have I missed something?

Maybe I'm missing something. I'm talking about his first visit. Were we talking about his second?
As for Gero's comments, I generally took them as standard villain posturing, if only because the evidence points elsewhere. 1- Gero seemed shocked by the level of power from SSJ, but he couldn't have been unaware of the state completely. He was monitoring (and cell-stealing from) the site of Freeza's landing. Initially he would have seen Goku go SSJ and wipe the floor with Freeza and Cold. Eventually 17 and 18 would emerge and we all know how that went. In the main timeline, we get 3 more artificial humans than in historic record, and the primary two are ridiculously more powerful than they initially were. 16 is even left out more or less, suggesting that Gero may have been trying to work on him or at least have him handy as a final option. In the original timeline, he probably would have destroyed 16 when he was deemed defective, or at least sealed him deeper in the lab (unless 17 just didn't care in the future and destroyed 16 before leaving).
But directly or indirectly, and admitted by Gero or not, something Trunks altered lead to Gero stepping up his game.

[Xyex]

If you're assuming that Trunks' visit to the past caused #16 to be activated, then we could just as easily say that Cell never came out of the ground. If that's all it takes to explain why a character did or didn't show up...

Uh, no. B can lead to D but A can't lead to 12. Trunks presence directly lead to the activation of 16 through his actions. Trunks did jack diddly squat to drag Cell out of the ground.

It also lead to him being more afraid of them, and shelving them in favor of models 19 and 20.

I've always figured 19 and 20 always existed. But Vegeta or Piccolo blew up 19 and was then killed by 17 and 18 before anyone else had any idea what the hell was going on. I've also never bought the Androids in the future being weaker than those of the past. I chalk that up to Trunks not realizing that the future Androids have only been fighting at half power.

Or have I missed something?

I don't know about Onikage but I'm refering to Trunks having the Z Fighters rounded up to fight the Androids and thus their group being able to chase Gero putting pressure on him and Trunks blasting the lab to try and prevent 17 and 18 from being activated.

Without Trunks the Z Fighters woudn't have known what was going on. Someone would have taken out 19 and then followed Gero but not nearly as closely or persistantly as in the series timeline. Gero would then have had more time to get 17 and 18 ready for release. Thus perhaps Gero in his more calm working conditions put 16 out of the way and he went unnoticed.

Or, if you want to go with the idea that 19 and 20 don't exist here then things are even more simple. Without creating 19 and 20 Gero would have done completely different things during those spans of time. Perhaps even effectively dismantling 16 in an effort to 'fix' him and thus putting him in such a state that activation was impossible.

Trunks presence alters the course of events for the Z Fighters and the Androids but Cell is a seperate entity in a seperate location uninvolved with the flow of events and unaffected by what they're doing. He'll emerge just the same as ever, he'll drain that first city just the same as ever, no matter what Trunks and co (or lack of Trunks and co) do with Gero and the Androids.

[desirecampbell]

But directly or indirectly, and admitted by Gero or not, something Trunks altered lead to Gero stepping up his game.

I disagree. If Gero had thought he was unprepared when he saw Trunks kill Freeza he would have done something about it - and he would have bragged about having such foresight. He brags about creating jinzoningen to destroy Goku based on all the data he collected, and that the Super Saiyan transformation would not change his opinion that he was superior. There's no indication that Gero would have lied about how he came to the point he was at.

Gero seemed shocked at the power of everyone. He hadn't been collecting data for the last few years, and had assumed that everyone's power would be lower than it was. Clearly he hadn't stepped up his game at all.

Further, if #16 had anything to do with 'stepping up his game' then when he ran to his lab for backup he would have activated him not #17 and #18.


-edit-

Uh, no. B can lead to D but A can't lead to 12. Trunks presence directly lead to the activation of 16 through his actions. Trunks did jack diddly squat to drag Cell out of the ground.

What exactly did Trunks do to cause #16 to be activated?

It also lead to him being more afraid of them, and shelving them in favor of models 19 and 20.

I've always figured 19 and 20 always existed. But Vegeta or Piccolo blew up 19 and was then killed by 17 and 18 before anyone else had any idea what the hell was going on. I've also never bought the Androids in the future being weaker than those of the past. I chalk that up to Trunks not realizing that the future Androids have only been fighting at half power.

I agree. I assumed that both attacks (Trunks' future and the main timeline) happened about the same way. Gero and #19 attacked an island, overpowered they retreated to the lab, killed when they activated #17 and #18.

At this point I assume that #17 activated #16, just like the main timeline. There's no reason to think this point in the attack is different.

Or have I missed something?

I don't know about Onikage but I'm refering to Trunks having the Z Fighters rounded up to fight the Androids and thus their group being able to chase Gero putting pressure on him and Trunks blasting the lab to try and prevent 17 and 18 from being activated.
Without Trunks the Z Fighters woudn't have known what was going on. Someone would have taken out 19 and then followed Gero but not nearly as closely or persistantly as in the series timeline. Gero would then have had more time to get 17 and 18 ready for release. Thus perhaps Gero in his more calm working conditions put 16 out of the way and he went unnoticed.

Maybe. But is there any reason to think Gero would be more calm? Or that he'd bother with #16? Or that he really had any extra time? #17 and #18 still killed him, assumedly just as quickly as they did in the main timeline.

Or, if you want to go with the idea that 19 and 20 don't exist here then things are even more simple. Without creating 19 and 20 Gero would have done completely different things during those spans of time. Perhaps even effectively dismantling 16 in an effort to 'fix' him and thus putting him in such a state that activation was impossible.

Again, this is wild speculation. Not an unreasonable thing for Gero to do, but we've no reason to think he did. He could have made tiny fruit-copulating attack drones - but he didn't.

Trunks presence alters the course of events for the Z Fighters and the Androids but Cell is a seperate entity in a seperate location uninvolved with the flow of events and unaffected by what they're doing. He'll emerge just the same as ever, he'll drain that first city just the same as ever, no matter what Trunks and co (or lack of Trunks and co) do with Gero and the Androids.

There are only two ways we can explain something being changed in the main timeine (from Trunks' future):
1. Something very specific is changed by Trunks, and that causes a direct change we can see.

• ie: Goku being alive at all, the Z fighters being stronger, finding

2. The new timeline has a change that is essentially down to randomness that has no clear cause-effect.

• ie: (if Trunks is to be believed) the androids being stronger, #19 and #20 attacking the island, #17 and #18's personalities

Even #17 and #18's 'homicidal' personality changes are under question. Trunks says they're different, not 'out for blood', well maybe not yet but let them drive around for a couple years and they start running out of things to do.

[Kid Trunks]

2.The new timeline has a change that is essentially down to randomness that has no clear cause-effect.

• ie: (if Trunks is to be believed) the androids being stronger, #19 and #20 attacking the island, #17 and #18's personalities

I would agree with this explanation. It just seems like the way Toriyama would have gone with it.

[Xyex]

What exactly did Trunks do to cause #16 to be activated?

Directly created the circumstances under which he was activated.

I agree. I assumed that both attacks (Trunks' future and the main timeline) happened about the same way. Gero and #19 attacked an island, overpowered they retreated to the lab, killed when they activated #17 and #18.

At this point I assume that #17 activated #16, just like the main timeline. There's no reason to think this point in the attack is different.

There's every reason to assume that the situation at the lab is vastly different. The entire chain of events leading up to that moment is different as is the very moment itself. Without the entire collection of Z Fighters only seconds away from finding him he wouldn't be in such a rush to get 17 and 18 going because his ass isn't on the line.

Maybe. But is there any reason to think Gero would be more calm? Or that he'd bother with #16? Or that he really had any extra time? #17 and #18 still killed him, assumedly just as quickly as they did in the main timeline.

Why would he be more calm? How about the fact that Vegeta and Piccolo, both of whom could likely kick his ass, even without the 3 year warning, aren't about 10 seconds from blasting in his doors? And 17 and 18 probably killed him faster and then simply split. These two wouldn't be the more docile versions of the series timeline.

Again, this is wild speculation. Not an unreasonable thing for Gero to do, but we've no reason to think he did. He could have made tiny fruit-copulating attack drones - but he didn't.

And Cell could have stayed in the ground sleeping forever, but he didn't.

ie: (if Trunks is to be believed) the androids being stronger, #19 and #20 attacking the island, #17 and #18's personalities

17 and 18's personality changes aren't a random change. They're a direct result of Trunks presence as stated by Toriyama himself. Trunks wiped out all of Freeza's men, Goku didn't. One (or a few, I can't remember) of said men killed their parents thusly creating their more evil personalities in the original timeline~

[Terra-jin]

Where did he say that? I've never heard about that before...

About the question why there's a Trunks in the main timeline: the time-machine has a certain behaviour that causes this. Notice that in his second visit, Trunks travels to the year 767. Since he departed from his own, original future, you'd think that he ended up in the year 767 of the original timeline and created a new timeline from there. However, since Trunks enters the already changed timeline in which the Z-fighters have prepared, this is not the case.
Instead, the time-machine doesn't travel to the 'current' timeline it is in, but to the 'latest' timeline that was created. Now, when Cell travels back (the year 763 to be precise), he also enters the latest timeline - which is the one where Trunks has appeared. In this situation, the 'extra' Trunks in the main timeline with Cell is an integral part of the history of that timeline.

This is proof that there MUST be a Trunks in Cell's first trip. This timeline can then develop the events that we see in the series, eliminating the need for a timeline in which there's a lazy Cell.

[Kid Trunks]

Instead, the time-machine doesn't travel to the 'current' timeline it is in, but to the 'latest' timeline that was created.

This is where the problem is. Your statement is right, but not completely (unfortunately). When Trunks goes back and kills Freeza he creates a new time line. And when he goes 3 years into the future of that time line (when the androids appear), it is the same time line. So this means that yes, when he time travels he does go to the latest time line created. Otherwise, he would have gone to the time when the Z-fighters were killed, instead of when they were prepared...

But then by all of this logic, Trunks should not be able to return to his own time with his mother, yet he does. So basically, 2 different theories of time travel have been used in this story, making one big mess that can't be made complete sense of.

[Thanos6]

Unless the time machine has a dimensional navigator.

[Onikage725]

I disagree. If Gero had thought he was unprepared when he saw Trunks kill Freeza he would have done something about it - and he would have bragged about having such foresight. He brags about creating jinzoningen to destroy Goku based on all the data he collected, and that the Super Saiyan transformation would not change his opinion that he was superior. There's no indication that Gero would have lied about how he came to the point he was at.

We can debate "would haves" until the end of time with this series, so I'm just keeping it with what we know did happen. Regardless of what Gero bragged about during his villanous monologue, the events were different in the main series and the only conflicting factor was Trunks' earlier presence. Even if I stop speculating on Gero's state of mind and you stop speculating on what Gero would have owned up to, we still have that left as a basic fact. Gero did X in one timeline and Y in another. As the Y events unfold, Trunks is constantly admonishing himself for having screwed up the timeline. To say "actually, Trunks didn't really have any impact on the things he was talking about" delves a bit into the fanon aspect of things. That's well and good, and fun to speculate on, but it is hard to have a serious conversation with the intention of mapping out a plothole-free course of events based on everyone's individual hypothetical scenarios.

I've always figured 19 and 20 always existed. But Vegeta or Piccolo blew up 19 and was then killed by 17 and 18 before anyone else had any idea what the hell was going on. I've also never bought the Androids in the future being weaker than those of the past. I chalk that up to Trunks not realizing that the future Androids have only been fighting at half power.

I agree. I assumed that both attacks (Trunks' future and the main timeline) happened about the same way. Gero and #19 attacked an island, overpowered they retreated to the lab, killed when they activated #17 and #18.

I have a problem with that, because Trunks says there is no historic record of 19 and 20. I've only skimmed the manga version once, so maybe they have a clue on this. In the TV special they directly say 17 and 18 launched the initial attack. This also coincides with Trunks' account. Since the Z Senshi in this period had no knowledge of the artificial humans' arrival, and they gave off no ki, the only way for them to find out would have to be some sort of media coverage or distress call. If that were the case, it is highly unlikely that 19 and 20 would spend time operating unopposed and yet leave no historic record of their existence.

And what is this "if Trunks is to be believed?" Why are we taking an ego-maniacal villain at face value yet calling Trunks a moron? Future Gohan, one on one, was a match for 17. They had to team up to overpower him. 18, in the main timeline, toying with Vegeta, seemed to be in constant control. Compare that to 17 taking significant hits and 18 even making fun of him about it in the future timeline.

Let me put it another way- 17 and 18, in the main timeline, were barely trying. Yet the manhandled everyone. In the TV special, 17 attempts to toy with Gohan and fails miserably. So unless we cook up some theories on Gohan just being that much more badass than anyone else we'd seen, we pretty much have to take Trunks' word. Why would Toriyama even put the line in there if it was false? It isn't like they re-visit the issue, and he wasn't writing Trunks with the intent of having us think he was an idiot. Everything Trunks noted seem to serve the story by telling us that events were unfolding differently. Saying Trunks was in error the whole time is kind of like saying "No, Toriyama, you don't know your own backstory." That's an ok stance to take I guess, but it is difficult to reach a canon-supported decision if we start from that view.

[Xyex]

Where did he say that? I've never heard about that before...

It's in some sort of interview or something. It's been cited here on Daizex before (hence how I know of it).

This is proof that there MUST be a Trunks in Cell's first trip. This timeline can then develop the events that we see in the series, eliminating the need for a timeline in which there's a lazy Cell.

I've considered this. And I hold it as a possible inexplicable paradoxical time travel related phenomenon to explain things. But my main issue is as to why Cell appears in Trunks timeline when, technically speaking, it shouldn't exist prior to Trunks entering it.

But then by all of this logic, Trunks should not be able to return to his own time with his mother, yet he does. So basically, 2 different theories of time travel have been used in this story, making one big mess that can't be made complete sense of.

That's easily corrected if he can steer. The machine just points to 'most recent timeline' on the back trip and then to 'originating timeline' on the return trip. Voila, problem solved~

I have a problem with that, because Trunks says there is no historic record of 19 and 20. I've only skimmed the manga version once, so maybe they have a clue on this. In the TV special they directly say 17 and 18 launched the initial attack. This also coincides with Trunks' account. Since the Z Senshi in this period had no knowledge of the artificial humans' arrival, and they gave off no ki, the only way for them to find out would have to be some sort of media coverage or distress call. If that were the case, it is highly unlikely that 19 and 20 would spend time operating unopposed and yet leave no historic record of their existence.

Did the main timeline ever get Imperfect Cell on video? I can't seem to remember. And he caused quite a bit of mayhem and panic....

Either way, it'd not be too difficult for someone to hear of explosions in a city and decide to investigate. Or there's always that slim chance that Vegeta or Piccolo happened to be in the area and noticed the explosions. And then with the high levels of damage caused world wide by 17 and 18 it's also not a stretch to consider that any such video footage was destroyed long ago anyway.

And what is this "if Trunks is to be believed?" Why are we taking an ego-maniacal villain at face value yet calling Trunks a moron?

Because while he's not a moron he is generally out of his depth the entire time. And there are factors presented within the History of Trunks special that can account for what he believes to be 'stronger' Androids.

Let me put it another way- 17 and 18, in the main timeline, were barely trying. Yet the manhandled everyone. In the TV special, 17 attempts to toy with Gohan and fails miserably. So unless we cook up some theories on Gohan just being that much more badass than anyone else we'd seen, we pretty much have to take Trunks' word.

Actually, for a situation like that, Gohan would have to suck. Majorly. Because the Androids he was facing weren't trying either. They didn't need to double team him and before overpowering and killing him 17 informs him that they were only fighting at half of their power this entire time. In the manga version 17 kills him solo while in the anime she helps out just for kicks. Once they went to full power they kicked his ass faster than 18 stomped Vegeta in the series timeline.

I chalk the whole "The Androids are stronger for some reason" stuff up to Trunks just being clueless about the fact that the ones from his time have only been using half of their power. Thus the ones in the past that are fighting at full strength seem to be stronger.

[Onikage725]

Did the main timeline ever get Imperfect Cell on video? I can't seem to remember. And he caused quite a bit of mayhem and panic....

It doesn't really matter, because the military attacks Cell during his fight with Piccolo. So it is safe to assume that Cell would show up in historic records in that form.

Either way, it'd not be too difficult for someone to hear of explosions in a city and decide to investigate. Or there's always that slim chance that Vegeta or Piccolo happened to be in the area and noticed the explosions. And then with the high levels of damage caused world wide by 17 and 18 it's also not a stretch to consider that any such video footage was destroyed long ago anyway.

It just seems like a lot of speculation without canon support. We're told that Trunks caused a chain of events that altered a number of things. We're told that there is no record of 19 and 20 existing, let alone attacking cities unopposed for a time, in the original timeline. I thought this topic was trying to organize the canon events and categorize the various timelines. It is hard to do that if we're going to seriously consider a fanfic-ish theory about an under the radar adventure in which Piccolo and Vegeta hunted down an as yet unseen 19 and 20. It doesn't even fit the sequence of events. They tell us 17 and 18 attack, the Z Senshi respond and are killed. How does this work if the Z Senshi responded to 19 and 20, were slain at or near the lab, and THEN 17 and 18 begin their rampage?

I chalk the whole "The Androids are stronger for some reason" stuff up to Trunks just being clueless about the fact that the ones from his time have only been using half of their power. Thus the ones in the past that are fighting at full strength seem to be stronger.

Alright, I'll give you that. Especially with the manga events being what they are.

EDIT: Actually, on more thought, I think it is still up for debate. the future ones may have been toying around, but so were the ones in the main timeline. And the Z Senshi were stronger than when they fought them in the other time (Gohan not withstanding). Mainly Vegeta, Piccolo, and Trunks (he should technically have gotten stronger from almost getting killed at the end of the TV special).

[Super Saiyan Turlast x4]

Isn't it possible that the Androids in the main timeline weren't using their full-power? Android #17 told Krillin to challenge them again when they improve, which doesn't sound like someone who was fighting with all of their powers. Now, #18, on the other hand, might've used close ot her maximum, but even that is up for interpretation.

After Future Gohan fought the Androids and escaped, he trained for a year, and was confident he could win against Android #17 using 25-33% of his power; so, it's likely that SSJ Gohan was more powerful then that particular #17. After #17 tells Gohan "I didn't even use half of my power in the last battle", he proceeds to attack him, most likely at his maximum.

Trunks trains for three years, and believes he's stronger then SSJ Gohan after this. That, by default, should put him above Android #17 using the amount of power he did against SSJ Gohan in the first battle. I also don't think the Androids of his time used their full-power, but I doubt the other Androids did, either.

[Terra-jin]

This is where the problem is. Your statement is right, but not completely (unfortunately). When Trunks goes back and kills Freeza he creates a new time line. And when he goes 3 years into the future of that time line (when the androids appear), it is the same time line. So this means that yes, when he time travels he does go to the latest time line created. Otherwise, he would have gone to the time when the Z-fighters were killed, instead of when they were prepared...

But then by all of this logic, Trunks should not be able to return to his own time with his mother, yet he does. So basically, 2 different theories of time travel have been used in this story, making one big mess that can't be made complete sense of.

You mean that Trunks should enter the future of the same timeline? Yes, but we can resolve this by saying that the time-machine makes a distinction between trips to the past and trips back home. While trips to the past follow the logic I've described above, trips back home always point to the timeline that the machine was from. This is fact (as seen in the series).

We don't know how this double feature works, but we can speculate that the time-machine has a dimensional navigator, like Thanos6 said. The machine might remember the distinct location or frequency or whatever of the timeline, enabling it to control where it goes. In this case, the time-machine was probably configured in such a way that it can revisit the past and return to the future.

This is the way it happens, as far as I can see it's fact. At first I thought desire's theory was in contradiction to this fact, but I think I now know what he meant. Desire, do you view the new timelines as having no past up to the moment they were created? If this were true, then Cell could indeed NOT travel to the 'latest' timeline, because Cell aimed for a point in time that doesn't exist across the span of the new timeline. In this scenario, Cell would enter the original timeline, without Trunks. Let me know if I understand you correctly now

So now, I'd like to know if we can determine whether or not new timelines have a 'past' or not. I think it's something that can't be determined, but perhaps you guys have some ideas? I think this question is equally important as 'does going to the future create new timelines or not?'

[Kid Trunks]

This is where the problem is. Your statement is right, but not completely (unfortunately). When Trunks goes back and kills Freeza he creates a new time line. And when he goes 3 years into the future of that time line (when the androids appear), it is the same time line. So this means that yes, when he time travels he does go to the latest time line created. Otherwise, he would have gone to the time when the Z-fighters were killed, instead of when they were prepared...

But then by all of this logic, Trunks should not be able to return to his own time with his mother, yet he does. So basically, 2 different theories of time travel have been used in this story, making one big mess that can't be made complete sense of.

You mean that Trunks should enter the future of the same timeline? Yes, but we can resolve this by saying that the time-machine makes a distinction between trips to the past and trips back home. While trips to the past follow the logic I've described above, trips back home always point to the timeline that the machine was from. This is fact (as seen in the series).

We don't know how this double feature works, but we can speculate that the time-machine has a dimensional navigator, like Thanos6 said. The machine might remember the distinct location or frequency or whatever of the timeline, enabling it to control where it goes. In this case, the time-machine was probably configured in such a way that it can revisit the past and return to the future.

But if it did have a dimensional navigator, Trunks would be able to go into the past of his own timeline and change its future. But he said he couldn't do that.

[Terra-jin]

Trunks meant that any changes of a timeline can affect its future, but not the future of the one that already existed. In fact, Trunks did go into the past of his own timeline, the first time he jumped with the time-machine. However, this caused a new timeline to be created, instead of his own timeline being altered.
That's one of the difference between other time-travel 'types' and Dragonball-style time-travel. In Back to the future, for instance, changes immediately act upon the past (even changing photos and such). This doesn't happen in DB.

[desirecampbell]

Gero changing plans
If Gero changed his plans, there's no evidence of it. Nothing is different from Future Trunks' timeline about the initial attack on the island: Gero creates androids numbered up to (at least) 18, someone attacks an island, the S fighters intercede - from there we see differences based on the fact that the Z fighters are stronger in the main timeline.

From Gero's own admission in the main timeline, he stopped watching Goku after he left for Namek, he didn't know about Super Saiyan. There's no reason to think that Trunks' appearance well after Gero had stopped caring would affect him.


If Trunks is to be believed
Trunks functions much like Kaioshin does in the Buu saga - shows up seeming to know everything that's going on and to be incredibly powerful, turns out to be wrong a lot and never actually helps in a fight.

A lot of the information we have about the future is from Trunks - and he's shown to be wrong (He says the future #17 and #18 were stronger than the main timeline ones - but there's no evidence of that, both sets simply toy with Trunks, he's in no position to judge). I mean, it's nothing to fault Trunks on, I doubt there's a lot of record keeping going on, and he can't really be expected to know every detail about attacks that happened when he was one that have since become common-place.


Lazy Cell
There's no reason to think that Cell stayed in the ground in Future Trunks' timeline. Just like there's no reason to believe that #16 wasn't activated, or that Gero and #19 didn't attack the island. There's no direct evidence to suggest that any of these didn't happen; all we know for sure is that Trunks has never heard of #16 or #19 or #20,

Would it be a stretch to say that Trunks' presence in the past had affected these things somehow? Not really, he actually says as much when he sees #20 and #19 - but again, Trunks just might not know how it actually happened in his timeline.


Historical record of Cell/#19/#20
I doubt that 'Lazy Cell' ever got far enough to attack a town, but even if he did - how good do you think the historical records are in Trunks' dystopian future, where people live huddled in the riuns of buildings?


Trunks can steer
I've always assumed it was simply 'time jump to the last timeline you were in', and that it's just how the time machine (or possible all time travel) works.