Note that it dates the GLASS, so is only an indication of the cars age, assuming the glass is original.If you are not quite sure of the year of your car, but the decade is known, just look for two dots in the TRIPLEX logo on the glass.My 75 GT has Sicursive side glass but a Triplex heated back-light with a code that fits the date of build of the car.This also works for any other make using TRIPLEX glass.The month of manufacture is now indicated by the dots over the word TRIPLEX according a rather complicated system: In 1929 Pilkington and Triplex formed a joint company to build a works at Eccleston, St. Pilkington gradually increased its shareholding in Triplex until by 1965 it became the majority shareholder.In Pilkington’s Queenborough factory on the Isle of Sheppey in Kent the original glass products were made under various brand names like Triplex, Sigla, Bilglas or SIV.
In the last picture you can see two dots over the "T" and one dot over the "X" in TRIPLEX. The date of manufacture is then defined by month rather then by calendar quarter.Safety glass windows for cars manufactured under the brandname TRIPLEX all received some form of manufacturing date code.This code was part of their trademark consisting of the word TRIPLEX combined with a circular formation around a triangular arrangement of the three X’s (= Triple X).A side issue of potential interest: Dating your car by its windows - based on the original compiled by Neil Cairns.------ "MG's made in the 1950's to the late 1970's can be dated by the 'TRIPLEX CODE' etched into the toughened glass.The last picture shows the later style logo with the word "toughened" with a dot under the 5th letter which would be the 5th year of the decade.This might be a later production replacement glass for the same car.I believe the tempered glass is a newer contrivance which can be stronger and may be manufactured in thinner plate to be less expensive. The last four pictures came from a 1969 Rolls Royce, and the word "SUNDYM" is apparently a trade name for tinted glass.Post war items are easily recognisable as from 1945 onwards the BS logo (or kite mark) was added below the original TRIPLEX logo. Notice in the first picture above the word AGREE with dots over the 4th and 5th letters.The year code can be found in the letter) word LAMINATED instead of TOUGHENED.To further determine the approximate month of production, look for a dot above the TRIPLEX word in the logo on the glass, whereby only 4 letters have been used for the coding: windscreens destined for the USA, whereby the year of manufacture was mentioned in two figures.