I believe that is more of a stake mark to help keep the drum tight in the sight tower, rather than a zero stake. I have seen plenty and this stake was aligned, but the rifle was not zeroed.
As long as it was on paper it was factory zeroed.
I remember going out to a range with fresh conscripts and shooting PM. Fixed front and rear sights, standard army issue. Range officer went first. Missed first shot. Small round target. A few shots later he told us to aim at 7 o'clock to hit the bullseye. It worked.
In real life if he had aimed in the middle of COM, shot wouldd have gone into the heart, instead of between the lungs. Close enough for a pistol with fixed sights.