"It may help someone else"
You're wrong. The ATF does not define or set precedent, the letter you received was merely valid for you and that pistol only. The law-abiding gun owner community can 'infer' the ATF's current mindset from little sonar pings like yours to the Tech Branch, but they can quite literally change their mind on this or many other issues at any moment (or at any direction from Il Duce). Heck, even this determination is merely a sort of defense against conviction, rather than protection from prosecution; you could still be put through the wringer and possibly convicted despite the presence of that letter at a later date.
Pinging the ATF for your own personal stuff is not necessary, and not a good idea on the whole. The reason for seeking a determination is so you can make a ton of these and offer them to sale, since that situation is one where your actions would be placed under a microscope, and getting clarification ahead of time is a good idea (case in point, EP Armory not getting a reissued ruling when they went to change their poly receiver layout). But in terms of just covering your own butt, the letter doesn't even do a very good job at that (it definitely isn't any type of guarantee or protection, legally) and quite often brings about conflict with previous rulings, since apparently these letter writers don't talk to each other. Whenever conflict like that arises, it invariably is resolved in the direction of greater infringement on us and discretion for the ATF. DON'T DO IT UNLESS YOU NEED TO FOR BUSINESS!
"A traffic stop later and the assumed legal shotgun landed him in prison"
Source/news link? Seems excessive, even for the ATF, unless there was other stuff going on in that traffic stop. Usually it would seem you'd end up out the value of the confiscated shotgun, whatever it cost, court/attorney fees, some time, and at least a few new pairs of pants from terror of the whole experience and lingering psychological effects. Also possibly an implied (not 'official/legal') restriction on your future firearms use or rights.
"I am no longer a risk taker when it comes to NFA regulations"
It sucks, but it is honestly something of a cost of dipping a toe in that pond. Between all the potential for shenanigans in the registry, the application process, and the whole configuration aspect the law poorly addresses, there is still ample room for someone to make your life miserable. Most especially someone who quite literally arrests you falsely under some misunderstanding (which is why we keep documentation handy, but it's not like they're required to read it before booking us). Read The Trial by Kafka to understand the types of forces at play here; at some point, you've done all the due diligence you can do, and at that point have to rely upon the sanity of your fellow man and the law of averages and bears*
TCB
*outrunning the guy next to you, not the bear. By which I mean that if you do an honest effort at abiding the law, those who do not will attract more attention than you will, keeping you safer.
TCB
. I have included a screenshot of the letter as well as the handstop picture.
