I know what you mean, about the knurling. As is the case with vintage Rolex, the little grooves in the knurling have different shapes depending upon the era of the bezel's manufacture, and there are people who can tell you about such things. I was reading about this on another forum recently because I was curious about the bezel on my 1675. Below is a pic from that other forum (posted by jasonlo213). In response to that photo, another user wrote, "Right is gilt era and pointed crown guard bezel. Middle is for matte era. Left is service for 1675/16750." I love that this sort of information is available, and it makes me appreciate these little details even more. [And I was relieved to see that the bezel on my watch, a 1675 gilt era with PCG, was correct!]