For whatever reason, I don't yet know???... But I can tell you this much, if you line the marks up perfectly, the front sight base will be canted...also, I think in the vast majority of cases, the mark on the receiver only, is perfectly centered and true... As for the barrel marks, some are perfectly aligned, and some are off... I think that the barrel mark was just a reference for correct barrel torque... I also believed, during early production assembly, it could have been assembled and then dismantled for some unknown reason, and reassembled, and then, on some, remarked??... Sight alignment, is a whole nother step! These guys were Germans, they though nothing of adding 5 extra steps to a one step process??
.. Best to all, til...lat'r....GT