Just another thought.
Roy Vail had his shop down in Warwick NY from the 40's through the 70's.
He dealt in high grade firearms, building custom guns and did some of the engraving as well. He, like many of the better 'smiths involved with high grade guns (and their customers!) of that time period did have connections with engravers (as well as gunsmiths and dealers/manufacturers) in Europe. He was and still is a well known name in the custom gun field.

Just speculation of course,,but being reletively close to each other, it's a possibility that the engraving job was done out of Vail's shop. Either done 'in house' or sent to Europe to be done by one of his contacts there.