Thank you Visionaut, I quoted the information from your linked thread below:
Liz. Sekurit means Licensed Sekurit glass. Sekurit was the original trade name Saint-Gobain applied to their invention of laminated auto glass in 1929. The manufacturer of this rear window was Vereinigte Glaswerke (VEGLA), a German subsidiary of Saint-Gobain. It eventually became the current Sekurit Saint-Govain Germany. Note there's no BMW Roundel at the top of this bug. This lack of the BMW logo in the bug normally indicates it’s replacement glass.
Duro-Glas was a trademark used for VEGLA’s licensed Sekurit laminated and tempered auto glass. Delodur was another. 1F is the specific version used.
DOT28 - All the Auto Glass Mfgrs are assigned a registration number by NHTSA. 28 was the number for Vereinigte Glaswerke (VEGLA) of Porz, Federal Republic of Germany. The required placement of DOTXXX in the window bug went into effect April 1973.
M1010 - M numbers are manufacturer glass model types (but NOT the part number. Two different parts can have the same M number.) 101 is the manufacturer model type for this rear window glass. The last trailing digit in an M number indicates if the glass is tinted or not. 0 indicates its clear, 1 would indicate it's green tinted, 2 that it's bronze-tinted, and 3 would be blue-tinted). FWIW, all my 76ers side glass is BMW Duro-Glas original green-tinted - and they all carry M101 (10 is the type ID, and 1 shows its green-tint).
AS2 - Indicates this glass has at least 70% light transmission but it doesn't pass all the impact tests like AS1, which is required for use in windshields. AS3 designates the glass passes less than 70%. All my tinted side glass is also AS2.
TF - ? I think this might be a Date Code, but I'm not 100%. All my BMW Duro-Glas side glass also carry the code TF, as does this rear window. So maybe TF = May (F) 1976 (T) production? Maybe not, but If so, then even though this rear window doesn't have the BMW logo in the bug, perhaps it's also original?
My glass reads:
DURO-GLAS-1F
LIZ.SEKURIT
^^^ D 291
****************
DOT28 M101 AS2
SOLID TEMPERED
TF
M101 is specifically what I was looking for, it is clear glass, DOT28 means it was manufactured from 1973 or later, my car is a 1974 and it also has TF so to add to visionary's notes TF does not stand for a single date. I would say that there are no differenced between my 1974 glass and his 1976 glass so possibly in 1973 when they went from "DOTXXX" to "DOTXX" they made the same clear glass for the rest of their production years. Depending on "when" in 1973 they made the change, one could also speculate that it is possible that all square taillight cars came with M101 clear glass.
It would be interesting for others to chime in on what original glass their cars have.
I will be posting this same post in Visionaut's linked thread to hopefully continue the discussion over there. Thanks again Visionaut!