It would have been interesting to hear what the Indian mechanics/minders in the background were saying about the sahibs on the Nortons! One of them seems quite amused so their comments may not have been complimentary!
Rob, I've seen one image of a pre-war India bike with a mirror - and the other one in the photo doesn't ! This is all that I have, from about a dozen...so it seems to have featured but not been the norm