These dials were made by Beyeler, for Rolex, and they were fitted in 1675 GMT Master within the 4, 2xx xxx to the 5, 6xx xxx case number range.
Which puts us around 1975 / 1977.
I didn't see any before, any after.
So, a three years production in a total of 20 years ( the life of the 1675 ) is not that much.
Best,
Nicolas