It doesn't matter when I can get them, as long as I can. Also, you can still trade for them in early game if you get it from someone who is farther than you. I did it in Sun to go through the main story with Buizel in a new file before. Theres no reason I shouldn't get to use the Pokemon I like.1. Regardless of who your favorite pokemon is, name a pokemon game where you can bring your pokemon up from previous gens before beating the Elite 4. For the purpose of the main game, it's no different. ALSO, this was a thing on 3DS too, before pokemon bank was updated to allow for the new gens each time.
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