here's an odder one. im guessing you unlock an enemy's page by defeating it, but after defeating the Superboss, all the individual enemy pages, even if i had never even encountered (I'm guessing it's cause of the Superboss, since one of the pages was for Postmodern, which the boss got that passive effect?) the Stamp Sheet still shows those enemies as missing tho, and the ChapterComp pages didn't appear.
(unless i'm an idiot and the individual enemy pages are given from the start and didnt notice)
I WAS playing with Saline, whose insanity kept spawning Delusions, dunno if that helps.