I've been known to delete my previously-saved version of a story (that wasn't even broken up into multiple chapters by LJ posting limits) and replace it with the AO3 version if and when I run across it later (whether because the author posted elsewhere first and uploaded to AO3 later, or because the author has differing usernames on different sites), as well as downloading the MOBI file to add to my Kindle if I think it was worth making easy to reread.

Also, very confusing when people like to change their usernames over time (or have different names on different networks) -- sometimes I gather it's a deliberate thing, wanting a new name for a new fandom, or having picked up a flock of trolls they're trying to ditch by dropping a particular username (I know at least one person this is true for), or having had non-fannish friends and family learn their username and having to frantically cover their tracks (I know two people who've had this problem).