I would be interested to know if anyone else can speak categorically on this, as I can't either. However, I strongly suspect that this is an example of a phenomenon often seen, whereby conversion standards & designations for modifications to equipment are accepted & approved, & in due course get into the VAOS. The fact that they have been given an official designation does not always equate with any actually being produced. Anther example might include the No32 Mk1/1 telescope, which was given the Optical Stores number OS1399 (the 2/1 is OS1400). The 2/1 was both produced de novo by UIC & converted from existing Mk2 scopes, though no Mk1's scopes were ever fitted with Mk3 scope drums (which is what the Mk1/1 was).
I do not believe any new build 4T's were ever produced (at least in the UK) after the WW2 contracts were cancelled in April 1946. PL referred in passing on a number of occasions to me about a few No4 Mk1/2 T conversions existing, although he never showed me one so far as I can remember. The L8 T designations allowed for the different variations in body configuration such as Mk1, Mk1*, Mk1/2 etc, as L8A1, L8A2 & so on, but how many (genuine) examples that exist is likely to be very small indeed (I've heard the figure of six mentioned but can't remember for sure). If you have access to a pantograph engraver you can put whatever you like on a rifle body....