How did [Manga] Vegeta train three years in the RoSaT and not pick up on Blue's main weakness?

[Bulma's Foot Masseur]

We know Vegeta overcame the "You can't transform into Super Saiyan Blue more than once in a limited timeframe" when he entered the RoSaT for six months between fights with Black, but how was he not made aware of this when he and Goku were there for three years prior to the Universe 6 tournament? Does stamina work differently in the RoSaT? Did Vegeta know about the weakness all along and just forget? Because I think Goku even asks "Why did you do that?" when Vegeta was trying to motivate Cabba, as if Vegeta should have known better or something.

[DSB]

We know Vegeta overcame the "You can't transform into Super Saiyan Blue more than once in a limited timeframe" when he entered the RoSaT for six months between fights with Black, but how was he not made aware of this when he and Goku were there for three years prior to the Universe 6 tournament? Does stamina work differently in the RoSaT? Did Vegeta know about the weakness all along and just forget? Because I think Goku even asks "Why did you do that?" when Vegeta was trying to motivate Cabba, as if Vegeta should have known better or something.

Plot Device. "Vegeta must be weak"

[LightBing]

Pretty sure he knew about the weakness. What he didn't know about was Hit's actual power and technique, which is why he took the gamble of weakening himself.
Even if he suspected Hit to be strong, taking into account his experience, being God Tier is very unlikely. He had been manhandling everybody in just SSJ until that point.

Another point to consider is Vegeta's priorities. He probably would rather lower his victory's chances by a huge percentage, if he could inspire Cabba to become stronger. He spent the whole fight tutoring him, it's very reasonable.

[Tectorman]

Wait. Did they train for three years prior to the U6 tournament? Because if that's not a thing that ever happened in the manga, then the "multiple use drops Blue's power" thing would never be contradicting it, right?

[TheUltimateNinja]

Wait. Did they train for three years prior to the U6 tournament? Because if that's not a thing that ever happened in the manga, then the "multiple use drops Blue's power" thing would never be contradicting it, right?

They did.

[TheMikado]

We know Vegeta overcame the "You can't transform into Super Saiyan Blue more than once in a limited timeframe" when he entered the RoSaT for six months between fights with Black, but how was he not made aware of this when he and Goku were there for three years prior to the Universe 6 tournament? Does stamina work differently in the RoSaT? Did Vegeta know about the weakness all along and just forget? Because I think Goku even asks "Why did you do that?" when Vegeta was trying to motivate Cabba, as if Vegeta should have known better or something.

In Universe, he knew, but he didn't really have a choice because it was still his most powerful form.

Out of universe, Toriyama likely wrote the outline where they train for 3 years and state they hit their limits. Go to the tournament, but Goku is 10x stronger in SSB for no reason stated in the outline but whatever plot device the writers could come up with... then had Vegeta job to Black, go back into the RoSAT for 6 months and suddenly whoop Blacks butt, despite hitting his limits earlier.

So to recap, in universe: shenanigans
Out of universe: lack of a quality foundation and other shenanigans.

[Steven Bloodriver]

We know Vegeta overcame the "You can't transform into Super Saiyan Blue more than once in a limited timeframe" when he entered the RoSaT for six months between fights with Black, but how was he not made aware of this when he and Goku were there for three years prior to the Universe 6 tournament? Does stamina work differently in the RoSaT? Did Vegeta know about the weakness all along and just forget? Because I think Goku even asks "Why did you do that?" when Vegeta was trying to motivate Cabba, as if Vegeta should have known better or something.

1) Blame those dastardly villains who are in charge of writing him!

2) Or because of being smug as duck all the time, Vegeta just didn't care?

[Bulma's Foot Masseur]

Pretty sure he knew about the weakness. What he didn't know about was Hit's actual power and technique, which is why he took the gamble of weakening himself.
Even if he suspected Hit to be strong, taking into account his experience, being God Tier is very unlikely. He had been manhandling everybody in just SSJ until that point.

Another point to consider is Vegeta's priorities. He probably would rather lower his victory's chances by a huge percentage, if he could inspire Cabba to become stronger. He spent the whole fight tutoring him, it's very reasonable.

Yeah, this sounds pretty likely. Stupidly arrogant but not just...stupid.

[TheUltimateNinja]

Pretty sure he knew about the weakness. What he didn't know about was Hit's actual power and technique, which is why he took the gamble of weakening himself.
Even if he suspected Hit to be strong, taking into account his experience, being God Tier is very unlikely. He had been manhandling everybody in just SSJ until that point.

Another point to consider is Vegeta's priorities. He probably would rather lower his victory's chances by a huge percentage, if he could inspire Cabba to become stronger. He spent the whole fight tutoring him, it's very reasonable.

Yeah, this sounds pretty likely. Stupidly arrogant but not just...stupid.

That still doesn't answer why he didn't bother fixing it when he had 3 whole years to do so.

[Bulma's Foot Masseur]

Maybe the assumption by Goku and Vegeta of it being a fundamental weakness went unchallenged until Vegeta was embarrassed enough to prove otherwise. I think it's been proven that characters can undergo generic training for years and it still be worthless compared to training with a very specific purpose in mind, usually after losing to a particular opponent. (See Golden Freeza.)

[LightBing]

Pretty sure he knew about the weakness. What he didn't know about was Hit's actual power and technique, which is why he took the gamble of weakening himself.
Even if he suspected Hit to be strong, taking into account his experience, being God Tier is very unlikely. He had been manhandling everybody in just SSJ until that point.

Another point to consider is Vegeta's priorities. He probably would rather lower his victory's chances by a huge percentage, if he could inspire Cabba to become stronger. He spent the whole fight tutoring him, it's very reasonable.

Yeah, this sounds pretty likely. Stupidly arrogant but not just...stupid.

That still doesn't answer why he didn't bother fixing it when he had 3 whole years to do so.

Because he couldn't: like Piccolo who couldn't go past 4xx in three years but got to 3xxx in a few months; like Goku who spent three years preparing for the Androids and didn't reached the grades or mastered the form. I bet there are more examples like this.

Super Saiyan Blue is still very much unmastered. The whole point of going back and forth with it and SSJG is because the form is still draining. Vegeta basically found a way to minimize the problem and grind-out Goku Black.

Blue is likely the Super Saiyan from with the highest skill cap of them all. Only SSJ3 competes with it.

[Tectorman]

Wait. Did they train for three years prior to the U6 tournament? Because if that's not a thing that ever happened in the manga, then the "multiple use drops Blue's power" thing would never be contradicting it, right?

They did.

Ah, my mistake. I guess I glossed over that part (I think I was looking for Spartan beards and didn't see any).

On-Topic: I can think of a few ways the "multiple uses" issue would plausibly not have come up prior.

1) Based on the one sparring bout depicted in the manga, we can surmise that while Goku and Vegeta trained against each other a lot, they kept it mostly at Base and sparred in Blue more sporadically. Ergo, fewer opportunities for the issue to manifest. (Also, I want to point out that Goku had Grade 1 SSJ for four years before it occurred to him to try to get rid of the restless feeling and make the form more natural. Vegeta may have had it for nearly as long. So it's easy to imagine this being another issue that just fell through the cracks at the time.)

2) The "multiple uses" issue manifests itself in the Tournament after Vegeta used it once to demonstrate it for Cabba (but otherwise did not do anything particularly strenuous or taxing) and then again versus Hit. That is to say, the tournament was plausibly the first time that scenario had ever cropped up. All the other prior times in the Hyperbolic Time Chamber, if there were a time where Goku and Vegeta would have turned Blue, then powered down, then powered back up again, they likely would have been sparring every single time. So they'd be fatigued. So when they go back to Blue, they would indeed be at diminshed power just like Vegeta was against Hit, but they probably would have mistakenly chalked it up to being tired from the earlier fight, rather than it being due to multiple uses in quick succession. Vegeta's demonstration to Cabba was likely the first time Blue had been used to do no significant fighting. And since none of their other power-ups or transformations have a power diminshment based on recent prior uses, they wouldn't think to check if Blue had such an issue.

3) Goku and Vegeta as SSBs are significantly more powerful than Super Buu and SSJ3 Gotenks were when they broke out of the HTC. So while they were certainly sparring against each other as SSBs, they would likely still be holding back so as to not accidentally break out of the HTC and possibly fire an errant blast out at the Earth. So they may have been suppressed on purpose (not to mention that, without a healer or Senzu beans, they need to be careful not to seriously injure each other, lest they lose the benefit of a capable sparring partner). And if they sparred as SSBs, then powered down and back up, they would still want to be below the point where they might break out of the HTC. So they may have suppressed down to below Super Buu's level from the much lower "second use" power level and mistaken that for progress.

"Hey, are you down to where we won't accidentally break out of here?"
"Of course, Kakarrot. Why?"
"I don't know. It feels like I didn't have to suppress as much this time."
"That just goes to show how much we're improving."