Can someone help decoding the glass date codes of 1957 Skyliner?
My glass date codes are 71, 75, 76 and 77.

I just guess the first "7" stands for year 1957. Is it correct and how to decode the second digit?
My car is made 1957-07-18.


pictures attached
Logo_safety_glass_quarter.jpg
side_w_L.jpg
Vent_w_L_code.jpg
Vent_w_R_code.jpg