To clarify - I didn’t state that silver marked by Puiforcat was retailed by Hermès, but rather that Puiforcat has been one of the manufacturers who supplied Hermès. In other words, Hermès outsourced silver production to Puiforcat, in addition to other makers, and marked the silver with their own mark. This arrangement suited both : Puiforcat was not seen as diluting their brand by marking for another retailer, however prestigious, and Hermès had the benefit of retailing well executed and well designed objects. As you undoubtedly are aware, in France after 1838 makers only had to stamp a mark for silver fineness, and the retailer could stamp a maker’s mark.
The relationship between Hermès and Puiforcat has been close; in fact Puiforcat is now owned by Hermès.