OK. great. That means I don't have to re-save any of my previously saved books. But as a result of going through this issue, I am rethinking my backup strategy anyway, which may make the issue moot for me. I now realize that restoring a library via the "add books" method may not be very feasible or time efficient. So I am considering doing a second mirror backup of the entire library locally instead of just keeping a mirror in the cloud plus manual backups. Or I may just abandon the cloud backup and stick with a local mirror which I feel is safer. At any rate, thanks again.
