Audemars Piguet

Does anyone know what the "BA" stands for in the reference number used by AP. I know a watch with "BA" is in Yellow Gold as "OR" (or rose) is rose gold and "ST" is stainless steel. Just no idea what the letters "BA" signifies in terms of being yellow gold... 

Boite Acier = steel case but you say it is yellow gold !

Thanks for your help but I am fluent in French as my wife is French 😂😂. "BA" does not stand for boitier acier which means steel case as "BA" is used for their Yellow Gold watches 🤷‍♂️

www.r-l-x.de "We kindly inform you that material code "BA" for the timepieces in 18-carat yellow gold has no meaning. Should you require any further information, please feel free to contact us at your convenience. Kind regards, Carlos Audemars Pig... 

Strange that the code BA has no meaning whereas the other codes seem to be logical 🤷‍♂️👍

But that was a really anti-climatic end to this thread, LOL!