Dave,
You have seen this lock up close, but I must ask if it is indeed an "N" at the end of the name?
I wondered if it was a "U" that had received a blow and made to look like an N. I Thought I could see the right side of a U.....
The lock Does appear Very mid 18th C to me.
It is a pity also that some of the Very nice furniture cannot be removed, as this is often marked with the maker when iron/steel is used.
One family so involved were the Brunons, of St Etienne. They made high end iron/steel gun mounts.
Jean Francois (1737-1784) would be a possibility.