> it wouldn't be surprising if page numbers were a solution to help printers not mix up pages.

It's an interesting idea. Remember they printed large sheets containing many 'pages', I think even in different orientations, which were then folded and the ends cut to produce a nice orderly codex for the reader. They were printing in a different order than the one you read in.

I do think they numbered the large sheets or similar, and you can find old books that retain that number, but I don't recall what it is called.