I think you right.
But....
However at Zorki-1 cameras there is one feature - during all periods of manufacture there was a quantity not used s\n. And such not used numbers were engraved much later, for example numbers xxxxx (5 digits) could be used while were engraved already xxxxxx (6 digits). Besides, there are also other non-standard models. To me in my trading practice, for some years there were such. In general to classify cameras by a principle 1a, 1b, 1c, 1d, 1e it is possible, but there are no 100 % of a guarantee, that the concrete camera, corresponds to concrete model Zorki-1X, and also concrete year of manufacture. For example - I had a camera to all external signs corresponding 1a (the button, bolts on the bottom panel, serial number xxxxx), BUT having speeds 25... 50... Thus the camera was absolutely new (in a box), i.e. It very much for a long time have presented to the person for any holiday, it to it has not taken advantage also it a lot of time has lain in a case. Also it was checked up by my professional photo-repairman and has confirmed that the camera was not opened, and there are no not what traces of repair or intervention in a design. I had some more cameras which are not entered in classification.
