I don’t think there’s going to be a definitive answer Boris. The Soviets were pretty serious about the quality of their arms industry so I can’t imagine they wouldn’t have proof tested and zeroed each and every one, but I’ve got nothing but intuition to back that up.
I do remember reading long ago that it was thought there were common ‘proof marks’ on the left side barrel lug (circle with a TK comes to mind, or maybe it was a circle П, honestly could be almost anything I suppose).