That's like saying a published book is not a verifiable source because I can't make more copies and pass those around to wouldbe checkers. If you don't have a copy of the book I used, you're going to have to borrow it. Some of the more addicted Wikipedians have even been known to *buy* books in order to use them as references!
You don't need to make a copy of a book in order to read it, you can find an existing copy - probably in the library.