Have you already configured your punchout catalog in production or test mode? If so, either way, after you do so, click on the Catalog name or Radio button and edit. Then click on Subscriptions. You should see your list of customers and you can click to view "Catalog Validation Rules". Granted, this may not be the holy grail 
but will give you an idea. As for UNSPSC, It could certainly change from buyer to buyer and I would either recommend sending them a list of codes in use or request as you have done. Once you have setup your punchout catalog in test mode, you can "subscribe" to your buyer(s) so that they can test and report back with any findings.
Screenshots:
Brady Behrman
p: (888) 623-2374