The last set of numbers under "PPG" will represent the date code on your glass. For instance where "X9", 'X' can be one (1) thru nine (9) to indicate the month of manufacture and the number '9' will indicate the year 1969. If the last set is "XX9", then 'XX' will indicate ten (10) thru twelve (12) for the month with '9' once again indicating 1969.
Russ
