Are they being moved around? I haven't been online for a while, so I didn't know this. What "other ages" are you referring to? As far as I know, some of the neighborhoods have Eder Tsogal linking books, and some have Eder Delin linking books. It's a random thing, but there seems to be fewer Eder Delin linking books for right now...not sure if it's a bug or intended. The other ages should still be accessible from the books in Relto or through the Nexus. If it's otherwise, it should be reported to Uru Live Support, via a ticket.
I hope that helps.