The first C-cases had OMEGA and the chronometer script at the top with Constellation at the bottom, just like all the dog leg and standard lug models. At the tail end of the 751 run in the early 70's, they switched and continued with the Constellation under the Ω logo at the top with the OMEGA and chronometer script at the bottom, which carried on into the 10x1 series. Therefore we call the last of the 751's that had the 10x1 dials transition C-cases. The only way to tell is if there's a divider between the day and date or not. 75x = no divider, 10xx = divider.
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