FIRST LETTER IS THE MONTH
SECOND LETTER IS THE YEAR
First letter is the month, second is the year. Number following hyphen it the day. So JZ-16 would be May 16, 1967. One of my co-workers lent me a Buick magazine recently and in it were the LOF glass codes for GM products 1963-1972, taken from Car Craft Magazine, December 1996.