Raimey is correct--sort of. Kennett refers to late 19th century proof being compulsory only in St. Etienne--and barrels were made in various other places. Then the Paris proofhouse was established in 1895. But on a gun such as the Guyot in question, with English barrels, proof would not have been compulsory--and did not become so until 1962. Again, per Kennett: "The most striking change in the 1962 law is the reestablishment of compulsory proof for all civilian firearms."
Regardless of the above, it is--at least in my experience--quite unusual to find a French gun without a full set of proofmarks. I've looked at quite a few and have never seen one. I expect that's because, at least from the beginning of the 20th century on, it is highly unusual to find a gun that did not pass through either the Paris or St. Etienne proofhouses.
