I went round twice collecting all 28 notes and no trophy. Have to start a new playthrough, because you can't return.
Were you playing in co-op, and were you host or the friend-for-hire?
I've been having the same exact issue. I've been playing solo, I even started a new game and it still wouldn't pop in the new playthrough! Let me know if you get it to work, and what you did to get it to work please!
@ justin2394 Have you tried manually syncing your trophies? A guide to doing this can usually be found online.