the codes are etched on the the glass - it's quite small, and although easy enough to spot with the eye, it's really tough to capture with a camera.
the code will read as:
XX-DMI-Y
- XX is the month written as either one, or two numbers
- It has been suggested that DMI stands for Donnelly Mirror, Inc (the mirror manufacturer).
- Y is the last digit of the calendar year
EG:
8-DMI-2
Would decode as August, 1972.
I believe that for the 1980 model year (or there abouts) the mirror was changed to a convex mirror, and the words "OBJECTS IN THE MIRROR ARE CLOSER THAN THEY APPEAR" was added - so in essence, there is no chance of the date code for a 1980 calender mirror being mixed up with a 1970 mirror (keep in mind the very earliest 1970 parts were manufactured in December 1969).
Here is a 1971-1981 drivers side mirror housing with the larger opening with which to feed the remote mirror cables through:
Here is my December 1969 mirror assembly:
And just because, here is my small selection of door mirrors that I acquired while trying to get a nice pair for my car:
/\/\ Notice that I have two 1971 drivers remote mirrors "loose" from their housings.
And if anyone cares, my search ended when I acquired an NOS passenger side mirror kit - complete with a December 1969 dated mirror - complete in the old gold & red Delco box!
Unless I am mistaken, I believe the gentleman who is selling off Steve Ames' NOS parts is the guy I bought it from.