To have the right answer for the initial question, you would have to know the loadings of each round. It is absolutely possible, if the loadings are mixed, to have all of the headstamps shown on a a belt with 14 rounds left. If from a Messerschmidt, the belt was certainly longer and this represented the number of rounds left when it went down.
I have read many times that commanders at almost all levels of fighter squadrons, and perhaps even individual pilots (especially if “Aces”) had a tremendous amount of say in how the belts were loaded for planes (or the plane) under their control. It was not uncommon to have a mixture of S.m.K., S.m.K.L’spur., P.m.K. and B.patronen mixed in a belt. Each of these loads would have different headstamps, although all rounds of the same loadings would probably have the same headstamps.
If the lot number of each round was shown, and they are reported lots, we could probably sort out pretty close what they would have been, although there are lot numbers that show up in as many as five different loadings (or perhaps more).
Of course, the point is, the headstamps are mixed because loaded belts for fighter planes were often quite mixed with different loads.