At the very least, anything that was already achieved will probably not track properly. This could extend to anything that has counters as well.
I started playing BG3 offline and only got it to launch from steam after I was 40+ hours in. I was expecting some achievements to start counting from scratch. Instead, my counters remained at 0/X. My bookworm achievement, even now, sits at 14/100. Those 14 are from a new game I made after I was able to launch the game from steam. This applies to multiplayer games too. Back when I was stuck to offline I created a character in a friends multiplayer game. I've read many many books in that mutiplayer game after I was able to launch via steam but it also didn't affect the achievement.
