This is the earliest Boizot advert that I have been able to find. I think it features the 1910 3 speed Boizot Tri-direct and the 1911 2 speed Boizot Bi-direct. I believe that the 1911 Boizot Bi-direct was a different beast from the Boizot 2 speed derailleur of 1908, and could be fitted to any bicycle.
I believe that the 6 speed option mentioned in the advert is a 3 speed Boizot Tri-direct used with a double chainwheel.
(Source gallica.bnf.fr/ Bibliothèque nationale de France)