Yeah, I've noticed some of that too. - Edit 1
Before modification by ranagrande at 22/04/2011 04:09:37 AM
. . .was how they'd ALWAYS be missing a few books from any given series. Not because the books were checked out, the library just didn't own them. I could never figure that out. I'm sure some books were donated to the library, which would make haphazard collections understandable, but it happened way too often for me to believe all of those partial series were donated. And if they weren't, which librarian decided it would be a good idea to purchase books one, five, six and eight? If you're building a collection as funds allow, at least buy in order. I'm sure there's a logical reason to be found somewhere (lots of lost/stolen books, maybe?), but darned if I know what it is.
I think some of it comes from books that libraries donate to each other. Like, if the people working at one library know that they have a lot of patrons reading a particular series, they might get several copies of a new book when it comes out. Then a few months later demand drops off and they no longer need multiples, so they sell or give them to other libraries.
It is certainly annoying, but if you request the missing books the librarians will often be able to obtain them for you. They might buy them to fill in the gaps that they were probably not aware of, or at the very least they might be able to get a copy to you through an interlibrary loan.