A lot of the better guns from most , if not all, of the makers were engraved by "outside engravers". "Inhouse engravers" were usually kept employed with standard patterns, but more importantly, the best engravers were usually self employed and received more for their work. Some started out as employees of a maker and went "on their own" later when their skill increased. Since they were known by that maker, they were often called upon for custom work.
Mike