"The History of Trunks" movie is canon because it connects with the main series and exists as thus because of events and one can say that Trunks' interference in the past was always meant to happen. Either way it proves that DBZ is a multiverse with infinite alternate timelines and Bulma's Time Travel tech is flawed as it can only alter the events of Another Timeline and not their own. The majority of the movies also fall within Alternate Timelines/Universes due to events and things within those movies. Such as Movie 8, Mirai Trunks is present, but also Goku and Gohan could both go SSJ but did not remain in that form throughout the movie, despite taking place within the 10day period leading up to the Cell Games as when they appeared leaving the RoSaT. Another instance is Trunks' outfit being different. Trunks was wearing Saiyan Armor before and after leaving the RoSaT, yet in Movie 8 he was wearing what he did when he first traveled back in time while retaining the longer hair. Other instances in other movies, such as Tree of Might, include characters being alive who're supposed to be dead during that point in time. So these are clearly instances of Alternate Timelines with events relative to those of the Main Story but do not connect with them in order.
Actually alternate timelines can only be created if someone disrupts it, please read.
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The full reason why i think broly wins with med diff.
1. I don't think that the movie is based on an alternate universe because remember, there cannot be an alternate universe without anyone disrupting it, example, the main universe was all Z fighters except trunks should have died, the sub universe ( The main universe of the series ) where all the Z fighters survived is because of the disruption of trunks.. The movie has no one disrupting it thus it being called " Non canon "
2. With the point i stated above, teen gohan ssj2 is far stronger than hs gohan ssj2, i see hs gohan ssj2 spc level.
3. Gohan who was at 50% ( But boosted by goku with WORDS , goku didn't really give any power, it was in gohan's imagination ) was matching SPC who was at full power ( Otherwise, cell wouldn't have lost even if vegeta, who was nothing to him, disrupted ), even PC was kicking the asses of the Z Fighters ( FPSSJ, Super namekian etc. ) and SPC is much stronger than PC ( Obviously ) This shows the obvious difference between ssj2 and FPSSJ.
4. Gohan being ssj2 on his fight with broly is still debatable since there was no lightning surrounding him ( The lightning serves as the ssj2 trademark for me because without it, it wouldn't be obvious if they were ssj2, specially for vegeta ) Either the artists failed to draw the lightning ( Which is easy ) Or just made a mistake, adding one bang.