Yeah, most of the books in the set were in excellent condition, so it might be that the previous lucky owner didn't chance upon this fault. Or he didn't feel compelled to chase the issue.

But thank you Willem! I will do exactly as you suggest. I think I'll dedicate part of the upcoming weekend for a thorough check up of the books, and then try the email address you gave and/or look up Paul's address! I'll let you know if anything came of it.