Here is a bit more history of the "Masterpiece" revolvers, taken from "History of Smith & Wesson" by Roy Jinks.
"Mr. Hellstrom, elected president of Smith & Wesson in 1946, and the first person not a member of the Wesson family to hold this office, insisted on a complete redesign of the K target models. The redesigned models were completely different from prewar models. They had ribbed barrels and were equipped with a new micrometer click sight which did not require that it be polished to the frame as did the previous style."
"The first new K Target model completed was the K-22 and the first guns were available for sale on December 13, 1946. In the advertising of this series, the factory emphasized the name Masterpiece, believing they had introduced a true masterpiece for the competitive shooter."
So, historically speaking, this is how the postwar target revolvers from Smith and Wesson became known as "Masterpiece".