Hello Judson,
One Kilo/sq cm is equivalent to 0.98 Bar. So this is a gun that is not proofed heavily at just a tad under 840 Bar. I do not know of J. Brunet. More than likely, he was a retailer who bought his actions or guns from the trade and just put his name on it. I bet that your gun has St Etienne proofs (the palms). Paris is a lot closer to Chartres, so he would likely have proofed the gun there if he had made it in his shop.
As for your remarks about heavy proofing, there is one reason: Marketing!
It became a seller's point to have heavily proofed guns such as double or triple proof, even on very high end (as well as relatively light) guns.
The Robust has a good name and is quasi-indestructible. So I would not worry too much about the proofing.
I agree with your comments on French guns. They are a lot cheaper than the british guns and are actually a lot cheaper here than in France. It is actually pretty hard to find Pre WWII guns in France as lots of them disappeared during the war. I would venture to say that the one you have in the East probably came back from Germany in 1945.

WC