Theres a difference between Generational pokemon and Regional Pokemon. Sounds confusing but listen. Houndoom, for example, is a 2nd generation pokemon, but isnt a Johto native pokemon, its a Kanto pokemon that was discovered during the events of gen 2.

This explains multiple Pokemon not being found in the wild of their respective "regions"

More examples

Farfetch'd - Gen 1 Johto Pokemon
Beldum - Gen 3 Alolan Pokemon
Murkrow - Gen 2 Kanto Pokemon

Does this make sense? Or am I just autistic?