The above picture was snapped by me at the airsoft company display, along with the CZ P-09s they had. I have to say I was moving quite quickly and didn't ask any questions.
I think you multiplied potential maximum penalties by factory of three...
Count one, manufacturing an unregistered SBR.
Count two, possession of an unregistered SBR.
Count three, failing to register an SBR.
That was the way it was described to me years ago by ATFE, although the discussion was about select fire firearms, although the last two seem to be the same.