I often wonder why libraries will have completely arbitrary books from a series. In this case the library only has books 9, 10, and 16. Maybe those are just the ones people have specifically requested for the library to purchase? If so, why did they request only those? This happens a lot both with ebooks and physical ones and has always made me curious. (This isn't a gripe, just an idle thought. I know I can contact them to request more.)