Thanks to Gary Kern for sharing this link containing the 1912 Couesnon catalog:

Because I fear that linked sites could disappear, I am directly putting the images on this page, and ask for help translating the French.

1912 Couesnon Catalog

One needs a mustache to play a Couesnon instrument authentically!

In an e-mail Steve Sklar said:
Starting in the 1920s Couesnon started the "Conservatoires" branding to try and get college level music students ... which did not work.