He doesn't want 50 species registered. He wants you to manually catch 50 pokemon.
They can be the same species, as I was able to get Charmander with like 15 pokemon registered since I caught over 300 nidoran for candy.
Yuck, the starters have different EXP groups.
Edit: should be fixed now:
https://github.com/kwsch/PKHeX/commit/76a2e4f527689d7d6ab58f5567a22727f9ed1a82
146/153 of Pokemon Let's Go. Last update before CFW becomes available for 6.2.0. Remaining Pokemon are Trade-Evos, Mew, and Meltan/Melmetal. Download directly from GitHub, not updating the attachment here until everything's complete.
https://github.com/ReignOfComputer/RoCs-PC/tree/master/29 - Gen VII - LGPE Collection