Just had a look. We have to realise two things here: only "factory fresh" bikes may be considered, and if you don't see the side logos, it doesn't mean that they are (or were) not there. The first census numbers where I can clearly see the twin BSA logos on the sides of the tank is the C4197xxx series. New logos from contract C/6654 onwards?
email (option): wd.register@gmail.com
I can pull the date back a little further, in War Office deliveries at least. To C41709767 (WM20 18753) of Contract C6126 which commenced delivery 9/5/1940. It looks as if earlier machines in this contract may not have had the double decals.
Oddly, I have no copy from the Ministry of Supply ledgers for BSA contract C6126 but I do have the "sister" Norton contract C6127 which shows an extra charge for "painting of WD Numbers". In fact, the practice of applying the WD numbers to the now vacant number plate positions began somewhat earlier.
Might it not be that earlier WD M20s had only the top logo as the space on one side at least was reserved for the WD Serial number in all its white-edged black-panelled glory and that once this changed, someone in BSA's Sales and Marketing Department spotted an opportunity to increase brand awareness ?
Were Irish Goverment export tanks identical to British at this time, or did BSA apply twin decals to those anyway ?
edit. I think that I may have come in boss-eyed after a long day and the tank logos are on the bikes either side. Oh well, a good try :grimacing: