That's odd.. I got a comment on Steam yesterday, barely an hour after I posted the game there (so I assumed it was someone who had already played the itchio version and only played the Steam one to get the achievements). It said they were able to get all the achis but one, end 12, and I checked and saw that, effectively, there's a mistake in my code for it. But the rest should unlock fine. Are you playing on a Mac computer, perhaps?
The unskippable credits are unskippable, sorry XD