@ Noahflash14 I got your back I've posted my thoughs elsewhere before, I bet next gen is when they will link those pokemon but not this gen for the sake of making it like the 1st gen before any others and all the pokemon were unrelated to other regions.
In Isshu it might be that there is no way to relate old pokemon and new ones through evolutionary/breeding procedures, which they might introduce in the sixth gen do I kindda make sense, like they said so many times they wanted this to feel like the 1st gen well what better way, and then in the next gen (6th) introduce items that will link pre 5th gen pokemon and 5th gen pokemon so it's like the 2nd gen. I hope I make some sort of sense, but then again 5th gen pokemon might not be related to previous gen pokemon, who knows what GF has up it's sleeves.
But I'll keep quiet until I see it happen in a few years if it does at all, then I'll be like "SEEEE I TOLD Y'ALL SO!" LOL j/k.