On reflection I thought I should explain better my thought process. The service replacement parts had the S2MS number until the early 70's at which time the S2MS number was dropped leaving just the list number and date code. The look of gold chromate finish on the picture carb with the S2MS matches that of the look of the later reissue carbs that Carls Ford ,Branda etc. started to handle compared to period NOS that I have seen and had. That is how I came up with the sequence of which came first in this specific case . Just my opinion.