You’re welcome. 
And it comes with experience tbh. I’ve made 90 lists thus far including the two above. My first few sets also contained some errors here and there. The more I make of these, the more accurate they’ll probably become. But even now I can still make some errors here and there. Only the people actually collecting the cards and investing a lot of time searching for certain cards can say which there are or aren’t. I’m messaged pretty often by people for whom I’ve made the list stating I’ve missed a card they recently discovered themselves, or one is in the list which doesn’t exist after all. I make these lists in 20-120 minutes depending on the Pokémon, so it will never be perfect.
And heck, even for Pikachu I discover new cards every now and then. 
Just two months ago a new Base Set Pikachu variation popped up which is currently incoming, and yesterday a new French Jumbo Pikachu was shown to me which I somehow have to find.
It’s similar as with all the recent rare cards that were first seen this year: the DPt-P Cresselia and Darkrai; the girl Trophy cards; this post of the 1997 CoroCoro Illustration Contest cards that was posted yesterday by @chok ; etc. The first Pokémon TCG cards were printed in October 1996, yet we still learn new things on a weekly/monthly basis, even for cards printed 20+ years ago. 
Greetz,
Quuador