I agree with the 'D' standing for the Drozd anti-tank missile defence system.
Did you know that the T-62D apparently is not equiped with the 12.7 mm DShKM anti-aircraft machine gun mount? Which makes it unique from the T-62M, T-62M1, T-62M1-2, and the T-62MV. So, perhaps, the 'M' in T-62 means 12.7mm AA. It seems to put a new twist to this topic. Terrible, really. Because from the same source it states that the Model 1972 was equiped with the AA, so this may be the beginning of the 'M' series. Which the game OOB covers excellently.
How's this: T-62s with the V-46-5M diesel engine (developing 690hp) are designated T-62M-1, T-62M1-2-1, T-62MV-1 and T-62D-1. See, the '-1' means that it is the V-46-5M diesel engine, not the Model V-55 V-12 water-cooled engine. Man, you would think that everyone knows this already.
But...what does it really mean game wise?
This might help:
T-62M / T-62M1 / T-62M1-2 / T-62MV / T-62D
Sheksna-
ATGM: Yes / No / No / Yes / No
Volna FC*: Yes / Yes / Yes / Yes / No
12.7mmAA: Yes / Yes / Yes / Yes / No
Reactive
Armor: No / No / No / Yes / No
Smoke
Launcher: Yes / Yes / Yes / Yes / No
Auxiliary
Armor
Hull: Yes / Yes / No / No / Yes
Auxiliary
Armor
Turret: Yes / Yes / Yes / No / Yes
I need to use Excel or something
I am not too sure on the release dates, sadly
But, really, overall, most of this info already is in the OOB.
*(The Volna fire-control system includes the KDT-2 laser range-finder mounted over the 115 mm main armament, which has a maximum range of 4,000 m, TShSM-41U sight, Meteor M1 stabiliser and the BV62 ballistic computer.)
Jane's Interactive Armour and Artillery