Note that any remakes of these games apply, to the same thing, so I'm not mentioning them unless I need to
Generation 1: No box art legends. The only legendaries are not version exclusive and therefore are mentioned in both versions.
Generation 2: While your versions legendary is mentioned more, you can still catch the other versions legendary in the post-game.
Ruby and sapphire: While your versions legendary is mentioned more, I tjink the opposite legendary is mentioned once by the not evil team when that leader thinks about what could've happened if they summoned their legendary. I could just be stupid though.
Emerald: All of the weather trio is mentioned and obtainable.
Diamond and Pearl: The opposite is mentioned by Cynthia's grandmother, allowing you to add it's data to the Pokedex.
Platinum: Dialga, Palkia and Giratina are all a part of the story and are catchable in the post game.
Black and White: Both Reshiram and Zekrom play an important role in the story, but you can't obtain the other versions legendary. I can't remember if you can get both dex entries in it.
Black and White 2: Kyurem, Reshiram and Zekrom are all part of the story. However, you can't get Reshiram in Black 2 and Zekrom in White 2:
XY and gen 7: No mention of the opposite legendary in the main story. In the postgame of sun and moon (maybe the remakes too) you can see the opposite legendary by going in this portal thingy.
Sword and Shield: Both Zacian and Zamazenta play an important role. However, you can't obtain the opposite versions legendary.
