During all the Speedmaster hunting, I frequently came across 1967 case backs marked "145.012-67SP" as well as the more orthodox "145.012-67" marking.
Also, Watchco were selling off what they described as NOS case backs with the "145.012-67SP" marking.
At first, I speculated that this may have indicated a service part but I'm not so sure about that now. And I haven't seen the "SP" on any other Speedy case back. It only seems to appear on the 145.012-67 models - not any other year of the 145.012 or on any other model ref.
So - does anyone know what it is & what it signifies (if anything)
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