What kind of dates would you expect to see on glass?

[67GT500#1594]

My car has a build date of 3/23/1967. It has the following dates codes on the windows:

Rear glass 7C
Driver's glass 7A-vent 7A
Passenger glass 6M- vent 7A

I'm 98% sure the passenger door glass is original based on the conditions of the interior door parts and hardware!

Was the back glass "SUN X" on all cars? I'm pretty positive it's original too.

Thanks for any clarification here!
Regards Matt

[JD]

yes, rear glass was tinted, all other not (no tint strip at the top of the windshield either - unless the car had factory A/C.
7A = 1967 January
7C = 1967 March
6M = 1966 December