Your original assumption is correct. The two phillip screws secure the interior door card to the door frame. The armrests are secured to the door card only. The picture provided by malcolm1 is missing the two phillip screw holes below the armrests.
So what I needing is where the two phillips screws located below the armrest are secured to the door frame.
I removed the door cards, but I can't see in the door frame the two holes where these two screws are fixed.
Giulietta Spider (750) & Giulia 2000GTV (105.21)