Yep; appears I'm at least partially correct. here's an instance of constructive possession under the NFA:

https://blog.princelaw.com/2009/7/8/nfa-and-constructive-possession-myth-or-reality

Below quotes taken from this here: https://blog.princelaw.com/2009/9/1/florida-man-arrested-for-constructive-possession-of-an-sbr/

And look at how the fucking ATF treated this good, decent, normal, law-abiding citizen, all over some chunks of wood & metal:

On August 27, 2009, Jesus Amador, Jr., was arrested by an undercover officer when he sought to sell his Heckler and Koch SP89 pistol. But, one can legally sell an H&K SP89, so what’s the twist?

Unfortunately for Mr. Amador, he was selling the H&K SP89 with the accessories that he collected for it, which included a vertical front grip and a shoulder stock. If Mr. Amador merely possessed the vertical grip, the pistol would have to be registered under the NFA as an AOW. However, because he also had a stock, the pistol would have to be registered as a short-barreled rifle, PRIOR to purchasing or possessing the shoulder stock and/or vertical grip.

Mr. Amador posted the following on the FloridaGunTrader website,

Well folks my name is Jesus Amador, you out there might just know me as Digitalage03, i recently met up with a prospected buyer for my sp89 clone pistol, well turns out the guy was a undercover cop and the reason he wanted to meet up with me is because he saw that i was selling the pistol with a stock as one of the accessories, which by the way it was never on the gun and it is legal to own, you just cant install it without a tax stamp, well anyways once i met up with him not only did i get slammed to the ground and had about 7 armed cops (one of which) had a loaded 12ga to the back of my head while on the ground handcuffed they also illegally searched my car and even had the balls to drive off in my car from private property to a public place so they can tear thru it before the towtruck came and got , Well anyone here that know thier laws about this know they are in serious trouble, considering that the basis of all this is a misinformed sherriff called Mike Scott. Anyone out there that would like to help in this matter not because of me, but because if you are SICK and tired off all these power hungry cops screwing with your right feel free to contact me at (239)961-4208 if you want to read the liberal BS version on how it happend google Jesus Amador Lee County. Also just for the record i at all times stated it was a pistol, never had the stock or grip on the pistol, notified the person it was illegal to put on without a stamp and even was going to assist in LEGALLY getting a sbr stamp thru a FFL , and of course i asked about if they where a florida resident as well as if they can legally own a gun. So in short i will have thier ass, any suggestions out there?

Mr. Amador even posted pictures of his mugshot and more telling, a picture of the SP89 with all accessories in a case. Most damning for Mr. Amador, other than being caught in possession of the SP89 with the shoulder stock and vertical grip is the fact that the case has a cut out for the SP89 to be placed in the case WITH the vertical foregrip, which would seem to connote, contrary to his position, that the SP89 was fitted with the foregrip at one point. For a picture of the case with the SP89 and accessories, see here.

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