"waterproofness" - The race was on to conquer the deep between Rolex, Omega and even Doxa in late 1968 - 1969 period. While it is true that the Omega Seamaster 600 "Ploprof" was the technology leader it was rumored that their price point was double that of Rolex at the time which proved to be an insurmountable marketing challenge.
I can't find evidence of that as we can see from the Rolex price list and the Omega price list. I would love to here what others think about why the Ploprof fell behind.
The price below from Rolex set at 80-100 pounds sterling in 1968 and the Omega brochure with a price of 104 Pounds sterling in 1972.

