I may be wrong but I seem to remember being able to date glass by a dot above or beneath a letter. Both 'toughened' and 'laminated' have 9 letters and the dot corresponds to the year of production, although I am not sure every glass manufacturer had this system. The lack of a dot indicates a year ending in zero. Not sure if it is possible to work out the correct decade though.
I remember stopping a friend buying a 'ringer' years ago because of this and I also find it useful to date tyres sometimes.