Incidentally JM, When I was researching the book, the wartime man showed me everything relating to the No4T conversion over the course of a lovely day. And when we got into the examiners room, now/then the rest room, he put his hand into a little recess on the dest..., a sort of letter opening, and pulled out several stamps including sone of the little 'T's and the original '51' stamps of the REAL S51! There was no 'S' there...... but not bad after 45 years!