If a pokemon is wondertraded, it is not registered to the pokedex

I received a delta kabuto, which I have not captured before, from wonder trade and it is not registered in my pokedex. Same with meowth, weavile, and beartic. It doesn't seem to relate to the specific pokemon, only to the fact that they were wondertraded. Suze pls, I don't want to have to capture all the boring 'mons myself.