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 is where two dots over "T" and one dot over "X" means August.
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.
One dot above T, R, E, or X gives the quarter of the year the glass was manufactured: T = Jan, Feb, March, R = April, May, June, E = July Aug, Sept, X = Oct, Nov, Dec. Nine letters make the word TOUGHENED, one dot below a letter gives the year of the decade: T = 1 O = 2 U = 3 and so on. Say your car is a 1950's MG, then TRIPLEX TOUGHENED, with one dot over the 'R' in Triplex, and the other under the last 'E' in Toughened, indicates 'April/May/June 1958' Below are some date code pictures.
The first (from previous page) is a 1950's vintage logo.