Pete, I think your dates may be off. I have an article on Charlin, in French, which states that they went out of business in 1968. The same article refers to the Maharajah of Patiala, and states that Charlin made him a pair of guns.

I have a Darne pamphlet from 1977 which shows 3 different models of conventional (top lever/break action) OU's.