Dex entries throughout the game series are the protagonists personal insights and thats why you continually have to fill up multiple pokedexes that should already have data on previously discovered pokemon. Its like your personal diary instead of some kind of scanner that automatically pops out data when it sees any pokemon like the anime. It would explain why each gen and sometimes each game had different dex entries for them all. and dont think about the anime pokedex cause i assume thats equal to the difference between the pokemons cries in-game and them saying their names in the show.