[quote=@Ganryu]
[@Maxwell] "The list of Pokemon available [u]for capture[/u] will be limited to the first 251 Pokemon"~ NeoAC

Eh, apparently just about anything anything goes for starter.
[/quote]

I'm not completely sure about that, though, since Heartgold / SoulSilver introduced some amount of Gen III and IV Pokemon thanks to the Safari Park and some route / Trainer reworking.

Honestly just using 251 Pokemon is a bit of a problem for a few players who want to collect same-type Pokemon. Not a lot of Ghost-types, Dark-types, Ice-types, and Steel-types. At least there's more Fairy-types to use, since some Normal Pokemon were switched.