On English Wikipedia, there's also [[Template:Infobox book series]] 648 [[Template:Infobox Medieval text]] 87 ... (All numbers just from the transclusion count)
There may be edge cases yet even beyond those. For example uncategorized stubs about books.
I don't know that I would say that there are at most 85,230. Perhaps though one could say that there are approximately 90,000 books.
I know the WMF has a stats team, do they just do things like visitors and the like, or would they be able to help find edge cases and get a more realistic number with this as well?
Thank you, Derric Atzrott