This kind of historical puzzle is always interesting.
The first point to make is that a large number of references to the meaning of a name doesn't make it right, because these references were probably all quoting the same source; very few authors do original research. A good example of that happening was the 'MG 151 cowling guns in the Bf 109K' myth, which I think originated with William Green in the 1960s but I have seen copied many times since.
So we need to find the original 'core references' to the alternative meanings of the 'T', and make a judgment as to the authority of each. I don't offhand know what these are (I am alerting Emmanuel to this thread so he can join in). I might add that just having an authority say 'that is the meaning' doesn't necessarily make it right, either. One book I have is a brilliant description of RAF aircraft gun development in WW2, by someone who was in charge of the programme, but he goes on to talk about the '40mm Aden'. Ouch. Even the best people make mistakes.
I have to say that I would take some persuading that the Yak-9T (or Yak-9K) was primarily designed for the anti-tank role for three reasons:
1. The references I have seen to its success talk specifically about air-to-air fighting. For instance, that the long range of the gun caused the Luftwaffe to change tactics, and that one plane was shot down for every 30 or so rounds expended. The description of the use of the NS-45 in the Yak-9K also talks about air combat; the plane was given to an elite unit who claimed one plane shot down for every ten rounds fired.
2. Almost all of the pictures I have seen of the ammo show it with HE rather than AP shells. I have never seen ANY reference to the NS-45 being loaded with anything but HE.
3. Ground attack was very hazardous as it attracted masses of ground fire, so planes designed or adapted for it needed and received extra armour protection. I have seen no reference to this with the Yak-9T or Yak-9K.
So, let's track those prime sources!
Tony Williams: Military gun and ammunition
website and Discussion
forum