As a team collector, for years now I've used Panini's "Missing Stickers" program to pick up the stickers I need from the NFL stickers set. It's not a set that I'm interested in opening packs, and it's been an easy way to quickly get the Cleveland Browns stickers I want without amassing a pile of others that I don't. I only recently realized there was a difference between the stickers released in Europe and the ones released in North America (difference appears to be just the back, not the stickers themselves)..
I picked up a few of the European 2020 and 2021 stickers and was logging them into my PC when I looked at the 2020 stickers to see the difference. I couldn't find any. Went back to the US set in the DB and realized that the 2020 collection I had was entirely the European version, not the American one. Then I checked the 2021 cards and found that the ones I had received directly from Panini were the US ones. Not sure why the 2020 version they sent were the European versions, but now I need to put together a US set.
Worse, I need to go through and check all the other stickers I've gotten from them (as I said, I've been doing it for *years*).