Working with my (mass market size) paperbacks, I have noticed that, for some of them, the copyright / publication history page includes the OCLC number.
I'm going to revive this old thread (obviously the OCLC link is working again - I just used it - and the "block" I reported in another thread was a glitch.) But I thought I'd revive this thread based on the new notice on the OCLC website that the Classify service is being shut down in January 2024 and apparently only subscribers will have access to the ability to look up DDC class numbers.
Delayed thanks to Orbiting Cat for fixing the access issue. A new one has arisen - it's now asking to verify security (the "are you a human" captcha) and it's not accepting the input. With the site ending free OCLC in January, this might be the end of that.