I, for one, haven't seen these before. They are definitely 1937 model year photos as we have the new style knee grips but exposed valve gear and painted tank panels. So September 1936 to August 1937 but I would guess earlier rather than later, unless someone can give a more definitive date from the inferior makes on view.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.