Yep, for example The Binding of Issac is item number 19966. But we only have 18854 listings, which means we are currently off by 1112 items. Its a database issue, the more dupes folks submit the further off we go unfortunately.
We had talked about replacing missing numbers with newly submitted items. But matt did some research and from what he found, database experts say its not worth the effort and just let the empty numbers hang.