Sweater Fish Deluxe, someone who I would also trust as a very early NGPC nut makes the following list in a thread here.
how can you tell the difference between games from the U.S. and games from Europe?
forum.digitpress.com
Sweater was a pioneer of NGPC information, but 15 years after that interaction with him, I have come to the conclusion he was mistaken.
While I can't prove they don't exist, besides Bust-a-Move Pocket, I have yet to see a single US insert snaplock. I have probably spent more time than anyone scouring ebay and here for these, and I have not seen any. I would love to be proven wrong, as it would be very interesting, but I think Sweater most likely had a mistaken memory about ESRB stickered games.
Select early games do have ESRB stickers on the first release English snaplocks. They are all hard to come by - so scarce that I have avoided talking about them as to not generate competition. I'm still missing some after searching for very long time.
I've seen increasing chatter on facebook groups about them, so I'm not surprised to see a topic here revisiting something that has never really been put to rest. Here is the list of ESRB stickered games I know of, and I would not be surprised if others exist.
Bust-a-Move Pocket (no sticker - US insert)
Metal Slug 1st Mission
Crush Roller
Neo Geo Cup '98 Plus Color
Pocket Tennis Color
Baseball Stars
Samurai Shodown! 2
Fatal Fury First Contact
King of Fighters R-2