Larry is probably right, I have a nicely made 16ga boxlock that is marked Ets Lien Chapu Callens on the right barrel; Paris-Roubiax-Lalle on the left one. It has Belgian proofs with a lower case d as proof date. It has a manufactures mark on the standing breech, I have some photos on my computer I will dig up if there is interest.

I learn something every day, and a lot of times it's that what I learned the day before was wrong