I found a reference (I don't know how authoritative it is - take it with a grain of salt) that explains the codes on the windshields: http://www.carwindshields.info/windshieldmarkings.htm
According to this, the DOT 20 windshields are made in Japan by ASAHI Glass Co. Ltd. and the ones with DOT 376 are made in the USA by AP Technoglass Corp.
The M number is simply the model number of the windshield and is unique only within the manufacturer. It does identify the type of construction, but you would need to have the individual manufacturers documentation to identify what's what.
The AS number identifies the optical quality of the glass. AS1 is the clearest.
My windshield also shows the manufactures logo (AP) which is consistent with the DOT number, and the brand name of the glass, "Lamisafe".
So, my guess would be that Camrys made in the USA will likely all be DOT376, and all the Camry Hybrids made there would have the same M834 number. All those made in Japan would likely be DOT20, with Hybrids showing M8K4 (nothwithstanding possible E or 3 instead of the 8 - I haven;t seen one myself). I do find the similarity in the M number between the Japanese-made and the USA-made intriguing.
Replacement windshields having a DOT20 or DOT376 number would be expected to also match on the M number. However, it is possible for replacements to have a different DOT number and still be equivalent glass - there's no reason that different manufacturers can't make windshields to the same specification. In those case, the M number would almost certainly be different. Just more food for thought.