Roy,
There are factory drawings for these 250, 350, 500, & 600cc 'winged' transfers. The same drawing/part numbers appear in the 1936-37 Aero parts list, for the 1936 models only, petrol tank section (ergo, not applied to the rear mudguard). However it does not say where on the petrol tank it was applied or quantity required. Not the sides as surely it would have turned up by now in a photo. I have yet to see a period picture with a view of the top of the petrol tank where one might a) determine it is present, and b) see if it was centered on the panel or perhaps up closer to the filler caps. I have seen one restored tank where they placed it in the center but no idea if they copied what was there previously or added the transfer on their own initiative.
They could have designed the transfer and then not used it or for only a brief period in 1936. However the fact it made it into a spares list printed in 1937 suggests they did actually use it enough to warrant inclusion. Or maybe they had a bunch printed and were trying to get rid of them!
-Doug
