«if one's an incident, two's a coincidence, and three's a pattern, what's four?» Concretely: Are the data here Carl Zeiss serial numbers - Camera-wiki.org - The free camera encyclopedia actually correct? In other words: I have to admit, I'm not an expert on this question, and I do not have THIELE's books at hand, which could perhaps answer this conundrum that I believe to have noticed recently. When we were discussing the different M42 Tessars recently — West Germany late 1960s / early 1970s, and East Germany mid-1950s — I found: Regarding the West German Tessar specimens in my possession: Their serial #s have seven figures, and both start with a «72» — which, I presume, could be quite probably the year of production (or placing on the market) of the two particular items. Regarding the East German Tessar in Raid's possession, and mine: Their serial #s have seven figures, and the numbers end with «54» (Raid's) and «53» (mine) — and again, this would fit the production year, cf.: Zeiss Tessar 5cm 2.8 adapted to ltm. What I found, is this just incident, or coincidence, or a pattern, let alone «what's four?» ?