Statutory associations are not typically recorded at the Registry of Deeds.  Deeded associations are, of course, but such associations aren't organized under the Private Ways law.

If a statutory road association needs to go to court to collect, it should probably be prepared to show that it was properly constituted (which probably requires more care to preserve records, now that associations no longer need to be re-constituted each year), and that the assessments were properly adopted by the membership.

You'd expect that a real estate agent would know of the existence of the association, but I'm sure there are exceptions.  Since the existence of the association isn't recorded in the property records, it's certainly possibly that a new owner could be unaware of their membership in the association.  But of course, they could be unaware that they live in a historic district, a water or sewer district, or a special tax district, too, as those aren't recorded either.  Statutory road associations don't so much "pass with the land", like an easement or a deeded association; they're more like a tiny town government -- once the owners vote to create it, it has its own independent existence until the owners vote to dissolve it.

It would probably be a good practice for road commissioners to drop a note to the listing agent when they see an association member's property go on the market, just to let them know that the property is subject to a road association, who the commissioner is, and what the annual assessment for the property is, so the agent can make sure prospective buyers are aware of these facts.  Wouldn't hurt to provide the same information to the new owner when they arrive, as well.