Triplex Glass Codes

Pre-war cars using Triplex Glass had codes etched into the glass - do all yours match?  If not then maybe a window or two may have been replaced over the years.

Dating Pre-War Triplex Toughened Glass 1929-1940

In the Triplex trademark the words TRIPLEX and TOUGHENED were arranged in a circular formation around a triangular arrangement of the three X's.  Glasses were defined by the quarter of the year (Jan - Mar, Apr - Jun, etc.) and the year of manufacture.

The quarters were depicted by a dot above the word TRIPLEX.  (The 4 quarters corresponded to the first 4 letters of TRIPLEX.  T=1, R=2, I=3, P=4).  The year was indicated by a dot under one of the letters of the word TOUGHENED (9 letters for nine years T=1931, O=1932, etc).  For 1930 the dot would be placed to the right of the letter D

if the etching looks like this then it indicates that the glass was made in the second quarter of 1934