Mk1 bezels until around 1972/73. Mk2 for a year or two starting with the last non big red sigmas until normal big reds came with mk3. I think the crossover is quite big. To me the use of mk2 bezels are quite short but what do I know..
Early proto pushers to 3.0m serial. Standard mk2 pushers until 6 million something.
Feel free to correct me.