>>38836171Thinking about it, aren't there already some oddities within the concept of "only 151" by the time FRLG came out?
In GSC and RSE alike, there's plenty of old-fashioned lore about Pokemon like Ho-Oh or the weather trio. So Pokemon that aren't in the Kanto dex have been known about for a while within Johto and Hoenn, with the former especially being culturally rooted in the way they live.
There's also Lance (and Clair) coming from Blackthorn City, and Bruno being Brawly's teacher, meaning people from the two regions did interact, or move from one place to another.
Wouldn't it be more feasible if in the FRLG-verse they did know of Pokemon not native to Kanto?