the 10 year rule, how common is it and how is it enforced

We've stayed in hundreds of campgrounds/RV parks over the years, and the only time anyone has asked what year our rig was at check in was fellow that had a relative with a similar model to our old Class C and he wondered if they were the same year. Some of the check in forms do ask for the year and make of our coach, but it's never been a factor for staying there. Sometimes they only want the year and make of our toad for access permit purposes.