I wonder if maybe Omega was using two grades of xtal in that case, i.e. "armored hesalite" with logo and something else in acrylic w/o logo? Are any of your NOS 50s sans logo non-water resistant dress-type models?
Or maybe this is a market-oriented feature--yes to the logo xtal in Europe and no in the States at this time for example?
Or perhaps these logo crytals were just being gradually introduced across the model lines and it took some time for everything to have them...
Either way, thanks everyone for your valuable insights on this relatively insignificant detail!
Best,
T.
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