I liked 4A a lot. I like the idea for 2D, but I'd have probably said misplaced ISBN to avoid being indirect. That said, book identification number seems really, really unambiguous.
Hmmm...I was wondering about that. To me (and it could just be the librarian in me), it's a pretty direct abbreviation. Maybe I just liked the clue too much to be objective about it!
I think, also, in my head when I wrote the clue, I got the letters mixed up, so it wasn't initially an anagram. It was just a direct synonym. I may rewrite it for clarity.