A quick timeline of Boisbertrand is as follows: 1882 Boisbertrand & Theilloud bought a factory known as 'La Fabrique de Montjovis' in the suburb of Montjovis in Limoges. In 1893 they moved to 5 Rue Neuve des Carmes into a factory now known as 'La Pepiniere' - 'The Nursery' In 1894 they teamed up with Dorat. The next chapter is unsure, by my research I believe that in 1903 Dorat died and Theilloud and Boisbertrand continued to operate until 1941. I have found reference on an American site that it was Theilloud who departed and Dorat that continued on.
Boistbertrand was associated with several different people during his years in Limoges as a manufacturer. His factory was not geared to export to America so my first go to reference, Mary Frank Gaston's 'Encycopaedia of Limoges Porcelain', has no examples of his mark, just a quick hand drawing of Limoges written within the banner.
An earlier mark, above, which is normally dated 1894-1902, I have found for Boisbertrand implies, by the initials B.T.D.,that it was Boisbertrand, Theilloud and Dorat. As you see it is very different from our mark so I belive our mark did not appear until Dorat was no longer around in 1903. Our mark generally appears with the years 1900+, and considering underglazing was not perfected in Limoges until the late 1800's i think the very early 1900's is a correct timeline for this mark.
Well over 100 years ago.