Bought books not in the correct library

Why some of the books I buy are available in the "all the elements" and not in the "bought books" library? (names of the libraries are as they appear in Italian)

It happens only for some books. The shop where I buy the ebooks is always the same, installation procedure remains the same, some books are loaded in the correct library, some are not, and they are available and visible only in the "all the elements" library.

Can I add the bought book to the correct "bought books" library? Apparently not...

Thanks for your help!

Andrea