Rifles that were otherwise suitable for T conversion but which arrived at H&H with the 'wrong' rear sights would have had a replacement fitted. IIRC Mk VII discovered a document concerning exactly this - the supply of Savage Mk1 rear sights to be used as replacements by H&H. I have noticed a number of 1943 dated BSA 4T's with Savage sights fitted, though I cannot recall seeing any 1944's - but if Brian has that's good enough for me. It follows, & is the case with the rifles I have owned or seen personally, that the 'S' on the cut-off block was missing, as these rifles with replacement rear sights were going to need re-zeroing once converted. The presence of the cut-off block 'S' indicates a rifle has its original rear sight on it still & so does not need re-zeroing (after 4T conversion at H&H). If a rifle has the cut-off block 'S' & also has a Savage rear sight, then I suspect it is quite likely the sight has been fitted as a replacement by an armourer or during a refurb at some point in its life.