Look at your FBA shipments; go into each one, and look at the “Contents”, and see if your items are in there.
If not, why did you send these? Was there just a stack of books, and you grabbed them all and put in a box? Were any of them labeled (with FNSKU)?
If there are books in the box with no labels, and are not part of the shipping plan, I suspect that your chances of ever seeing them again is pretty close to zero. If you put a label on them, then it will get scanned into the system as whatever title is associated with that label, so if they don’t match, you have a problem. If you labeled them correctly, but they are no longer listed as FBA, then you should get a “Stranded Inventory” status, and should be able to recall them (or perhaps just change the listing back to FBA; not sure what might happen).
A lot of the answer comes down to why you sent in books that are FBM.