@Wood
As far as I know, the Pentagon estimate were done by counting how many destroyed vehicle and then times it by the appropriate crew, so when a T-80 was destroyed and shown, they will list 3 killed. They will ignore other casualty report that may also be true and put it in the "Maybe file" Say for example, if you have 3 T-80 and say 20 infantry pushing up, and that convoy is intercepted and the Pentagon was shown 3 destroyed T-80, then they will estimate the casualty as 9, even tho some or maybe all the infantry may also be casualty.
Only individual casualty they count is body, so basically no body, no one dies
A more closer estimate is to estimate the effective combat strength, which last report I read put 60% of the entire original invasion force as "Combat Ineffective" category, which mean 60% of Russian unit suffered 20% of casualty, which would make the casualty number closer to 10,000. But then that was 4 or 5 days old.