Making A Pokemon Not Register In The Pokedex

[ThyBikerGuy]

I'm wondering if it would be possible to make it so even after the player encounters a specific species of Pokemon, that species is not recorded in their Pokedex until after a certain point in the story where a flag could be switched to make it retroactively register. It would be fine if it didn't retroactively get added from the previous encounter, and this doesn't have to account for catching the Pokemon, simply encountering it in battle. I've been brainstorming and have been unable to figure out a way to achieve this effect, but I feel like it has to be possible.

 

[Baertierchen]

The cheap way would be to create the same Pokemon as two different entities, so their names and everything are all the same, but their ID's (that are not shown ingame) are different, and you only list one of them in the dex .pbs.
To register it in the dex via event you can use the script "$player.pokedex.set_seen(:NAMEOFPOKEMON)".
Although a bit cheap, this should achieve the desired effect I think.