You can date your 1930's car from the codes etched into the Triplex glass
for more complete information see this page
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.
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