The last 2 digits of the serial number were applied to identify which bits belong to which pistol. Initially, at DWM, a lot of hand fitting was needed to get anything to work smoothly.
Later on, with improved production techniques, the need to number parts to the guns was no longer required, because those parts did not require hand fitting.
In the 1970s, Mauser only had to keep the barrel/receiver and the frame together (numbered), the rest of the parts would just interchange without issues. So no small parts got numbers at all.
So the numbering is not a sign of meticulous quality. It is a sign of bad quality