Y6444 is a 1933 to 1935 frame. If you read the blurb on the Bonhams site you will see that they were advised that the frame on that bike is a later type. So the sprint special probably has the correct frame with the number transferred to the other bike.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.