>>49792773Easy. Kanto is actually a shithole and were denying the existence of Johto Mons inside their borders after the war and attempting a to propaganda that only their most local Pokémon were the only ones that existed to keep their trainers inside their borders, FRLG and LGPE takes places in alternate universes where they have warmer relations with Johto/Hoenn and Alola respectively which allowed travel and discussion of the pokemon in those regions, the girl talking about "Munna" or rather the "Flowerpatterned Pokémon" is a Unovan spy doing a Psy-op to undermine this and occasionally the Gov propaganda machine fails to cover something up.
Sinnoh was deeply ashamed of what happened to their lords and the Hisuian variants they decided to cover it up in shame, only leaving traces that positively depicted their History, that meant covering up their existence of Pokemon that had migrated into different regions.
Us having them "revealed" is just going into regions where people acknowledge the existence of these Pokémon or have them mentioned due actually being relevant Moving from less dystopian regions is why we no longer get the "National Dex" and just a region one that is acknowledged to be region specific.
This is also why the National Dex was growing the way it was, it is actually Kanto propaganda as we can see in how Kanto-centric it is, so even when they are forced to acknowledge other Pokémon they will always consider Kanto ones first.
We can also see in PLA that the earliest PokéDex projects were about staking out the local land for survival reasons, so even if seen in a different country it would just bloat a necessary survival encyclopedia with trivia for your own locals.
Effectively we can conclude that the National Dex is what Oak is out for, but he cannot acknowledge it in RBY and the following games are him and his fellow professors doing a cooperative effort to organize the finds each individual region has made, but not all have the same info.
