So you were issued a stamp the very second the ATF issued their ruling?
Or were you in possession of a now illegal SBR for a period of time before submitting and being granted your tax stamp?
Unless you had that stamp the second their new ruling went into effect, you applying for a "tax free stamp" is a defacto admission you were in possession of an illegal SBR.
Stop thinking like the ATF is a rational and well meaning institution....they are psychotically analytical with a history of murderous intent over petty reasons, and will look for any loophole they can to fuck you over.
The ATF is that coworker of yours who read 'The Prince' once in highschool....and now looks for any reason to fuck you over because he thinks it makes him look better and more competent.
You make a typo, he tells the boss.
You spend and extra 2 minutes on break, he tells the boss.
You tells joke, he takes "offense" and tells the boss.
....that is the ATF.....