Correct with the AR pistol. However, my lowers are pretty much all standard (magazine adapters can come out easily), so the engraved one will stay as the SBR lower... other stocked ones for rifles, and braced ones for pistols. Easy peasy.
The way I see it, you can’t go back to a firearm if you add a stock. If that were the case, I should be able to pull my 870P, and create a firearm (ATF has stated as such since the Shockwave came out). For people to make their own 12 Gauge firearms, it tends to require a virgin receiver.
It is a stupid concept, like the once a machine gun, always a machine gun... but that’s they game they currently play. I’ll play... at least until the overnight “you’re a felon” round.