Could you please tell me why this has both reference: 146.009 y 146.010 when all the others I seem to look at have one or the other? Seller also has another with same case-back.Thanks Peter.

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That's fairly common. Several models had that from the mid 50's into the 70's.

Seamaster caliber 751 from 1969:



Constellation caliber 354 from 1954:

 

Thanks a lot

 

No worries. It's one of those things you'll eventually know.