Regarding audio books from our public library: It seems that of the many books that are downloadable, very few are actually available. We have to wait for books to become available, because they are already "checked out", so to speak.
I'm afraid we are spoiled by the audio book paid membership thing. There's no waiting list for books, so we can download any book they have when we are ready for it.
It used to be a lot better at Audible.com before Amazon bought them out. We could download 12 books(1 year allotment) all at once if we wanted. Now we can only download 1/month, but the good thing is, if we don't like it we can exchange it for another using the same monthly credit. We can accrue as many as 6 or 7 books before we go on a long road trip.