Hi Eddie,
There are a lot of conflicting comments about the Breguet serial numbering system and I have never read anything from Breguet themselves. As far as I am aware the letters do not relate to specific years of production.
The numbers generally cycle between 250 and 5500 (although some have posted images of watches with higher numbers that appear to be authentic). The 3 or 4 digit numbers are printed in the cartouche on the dial. Each new dial gets the next number in the sequence. Breguet do not publish production numbers but it is probably in excess of 15000 per year, so they are going to go through more than one letter in a 12 month period.
Engraved on the watch case is the same ‘dial’ number plus an additional letter. So there are watches with the serial ‘numbers’ 3573A, 3573B, 3573C and so on. This is how completely different series of Breguet watches can sometimes be found with the same dial number. Some collectors even chase Breguet’s with the same dial number (although different letters of course)
Because of the random nature of the numbering system it is not possible to infer production numbers, particularly of individual models.
This numbering system does not apply to the Type XX or Type XXI collections.
If anyone can get a definitive answer from Breguet, please post it here!
Regards
Andrew