I shouldn't have added to the confusion. :D
As soon as any receiver is assembled, I am REQUIRED to log out the receiver (i.e. "other") and register it back in the books as whatever it's built as, and there's no turning back at that point, even if I strip everything off the lower, it remains registered as a rifle or pistol or SBR or whatever.
That's the reason I keep almost all of my lowers in their unassembled form, and only assemble our shop demo units for display. That way, they remain as "other" until a) it gets assembled into a firearm, or B) it gets sold as a stripped "other" lower.