Postby blakstone » Thu Sep 17, 2015 10:58 pm
One point of clarification: the Paris assay office was distinguished by the absence of a distinguishing mark (called a "différent"). That's why this swan mark seemed unusual; all the ones you've seen before without the "P" were from Paris. The différent "P" was used in the assay office in Pontarlier (Doubs département), which was in operation from 29 Mar 1865 until 1 Jun 1933. An office was established there precisely to accommodate the imported watch trade, as it was only about 8 kilometers from Swiss border.
Hope this helps!