Per some "open source" (usual disclaimers apply) calculations the Russians had only around 1500 T-72s in reserve (around 3400 counting active and reserve) - which seems pretty reasonable IMO.
Also AFAIK L/DPR forces have been officially integrated into the Russian armed forces, apparently recently mobilised are now in the lowest position of the totem pole (except convicts i guess).
These estimates from our side - nobody knows how many t72s russia has. 25000 were made.
I don't know if people remember that rusi article about industrial warfare and how they said they were surprised russia had more cruise missiles than estimated,ie,why we thought they would run out by summer last year.
We wouldn't be sending our frontline tanks(that we need) if russia was running out of tanks. Likewise,if they were running out of missiles,aircraft,etc we wouldn't be sending our patriots,samp/t,etc to the frontline.
My concern is how much have we underestimated chinese stockpiles of missiles,tanks,etc? They outpace most of the world in making things.