I do not live in CA... I am actually from PA where we do not have a "registry".
But they way I understood it was when buying a stripped lower... and intending to put a pistol buffer tube on it... and a short barreled upper in means of making an AR-pistol.... when one was purchasing the stripped lower it would have to go both on the 4473... AND the Application of Sale for a handgun.... seeing as it would be configured as a HANDGUN, not as a rifle with a stock.
I see what you mean with Constructive Pocession... although stupid... I guess it does look like I would be attempting to break the law. I guess I will just wait until I buy a AR Pistol lower to build the upper.