Here is a nice example of the 1967 GMT 1675 with the MK1 dial. It was the first transition dial from gilt. The way you can clearly see a MK1 dial is from the fact that the E is a long E in Rolex. Basically this means that all the three ends of the letter ...
I'd say that the GMT gilt era ended with 1, 6 xxx xxx serial numbers, which corresponds to '67. I saw a very nice '67 Gilt GMT with SR 1,6xx xxx. This one: Now, knowing when started to appear the MK I matt dial, that is another story. Certainly in '68. Pr...
You are correct. The serial numbers are always hard to go by as we have no real official record. So i would agree 1,6xx,xxx is still solidly in the 1966 - 1967 era of the Rolex 1675 GMT gilt. It always great to have examples so that we can prove our facts...