In regards to 2) above, many publishers do include this information. It's called "CIP" (cataloging in publication, I believe). Many of the cataloggers that I've known scoff at using this info though--it rarely meets their needs. University libraries often adopt the Library of Congress classification while public libraries commonly adopt Dewey Decimal classification. Even within each classification there can be room for disagreement or "doing it differently" for reasons that are relevant to your library, but not necessarily relevant to another library.

Disclaimer: I am not a librarian, but I worked in library automation for 18 years. The libraries that I worked for were all OCLC members. I've never catalogged, but I have loaded MARC tapes from OCLC and worked with cataloggers over the years. A good catalogger is anal-retentive, detail-oriented and cares very passionately about their work.