Webley merged with Scott in the late 19th century. I'd expect that any gun made any time after the merger would have been noted as "W&S" in the A&N records.
I lucked out, to a certain degree, with the information I got because the individual who ordered it happened to have been knighted, was a WWI hero, and from a fairly prominent British family. Even then it did take extra effort to run him down, and the initials on the motor case were the real clincher, along with the date of the order and the buyer's military rank. I also received pages from the period A&N catalog, showing the model of the guns I bought, and allowing me to compare them to other contemporary A&N offerings.