That chart is next to useless on Speedmasters, and anything at all really post 1990. Most of the on line charts are.
There is an overall pattern but with certain models Onega has been sequential within a range so there are jumps. 53.4m on a Reduced is around 1993 give or take a year but to be sure you would need to research other examples of a given model, look at intro dates etc. I keep date info for my watches, some of it calculated/estimated.
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