Easy there. It is my understanding from reading that and discussing it when it was released that an AR pistol can go back and forth, but a stripped lower that is a rifle first is always a rifle.
That is my understanding as well.
If it starts life as a pistol, it can go back and forth between pistol and rifle.
If it starts life as a rifle it must remain a rifle.
I know that does not make a lot of sense, but it is a government agency you are dealing with.