Someone mentioned that until a lawsuit is brought, things are a little murkier..
Even if the reg is pegged to a certain year, there are other ways these things are gotten around. My main grievences with NFPA don't have anything to do with rocketry but with "code enforcement" and specifically how GP materials find their way into building codes so fast. With buildings there are state certified inspectors that issues pass/fail marks when it comes to building codes and things are a bit more sloppy than "this is the law, this isn't." So regardless it's prolly a good idea to keep to what it says unless there is a clear reason to deviate, and in that case it would be good to consult with a legal team as well as local regulators and officials, which I'm sure motor vendors do.
The NFPA regulation also doesn't mention the inner workings of "certifying authorities" such as TRA and NAR as per the original question of what steps are necessary for a vendor to ensure a customer is a certified user. I'm sure a lot of that validation falls on the agreement between the certifier and the dealer. Certifier says "yes this person is certified." There's probably a lot of specifics in there that I have no idea about, but I would assume the policy of exchanging that information is probably up to NAR and TRA to decide on best practices.... at least, until there's a problem and then some govt agency might decide to step in and add paperwork.
I can't think of anyone better to answer that kind of question than Steve. And I would imagine there are probably lawyers on retainer to answer questions when the club brings them up.
Nothing is simple when it comes to navigating US law.