IIRC, T-80UD in Reguments are fictional and for balance. All Soviet T-80U/UD tanks remained within Soviet borders till USSR dissolved, mostly around Moscow or in SIberia (there are rumors about GSFG usage, but no proof surfaced so far).
I believe that Regiments uses UD due to ~700 being produced by 1991, comparing to ~480 T-80U, units with them being slighlty closer to Germany, and original unit model being based on UD version.

Interesting, I was under the incorrect assumption T-80Us were in GSFG service. It makes sense, as IIRC the T-64A took nearly a decade to leave the USSR due to teething issues, and I suppose the T-80U was a similarly advanced tank.

Still, that is unfortunate, I feel as though the T-80BV was plenty good enough to stand as the only tank available, and them not including any Soviet T-72s was something I appreciated due to most games incorrectly assuming the T-72 was in GSFG service. I bet they could have included T-80UDs and T-80Us in a future DLC/update to represent reinforcements, similarly to how they included the new T-72B.

Also the lack of T-64B is unfortunate, as that is my favorite vehicle and I think the T-64B1 is a bit over represented in the game.

AFAIK GSFG did have T-80UDs in 1989. It would be very weird for the dev to respect the T-72s not being in GSFG only to put a tank that was never in GSFG instead.

And yes UD is the more produced variant by a long shot.

Edit: Asked some people who know more, and the best answer I’ve got is a maybe. Might be the same category of the BMP-3 as a March to War unit (meaning a vehicle that is lore wise rushed into service because of the war).

T-80UD (and BMP-3s) were not in Germany... but the train infrastructure to carry them were. If even France could come to the party, it is not a stretch of the imagination.