I just read another headline about another ancient stash of classified papers, but I haven't read the article. It could be that when the Trump thing happened everyone was told "go check your own papers and lets get this all cleared up." The fact that Trump tried all sorts of prevarication and resistance to returning papers the Archives knew he had means he committed a crime where other omissions of returning may be just an oversight. Makes it harder for the AG to make a case, though.