I paged through the Standard Catalog of Smith and Wesson last night and did not see anything regarding the ampersand change. My guess is that it might be different for the pistol slide than for revolver barrels and my other guess is that whenever the change was made might not be the most accurate dating method. Especially in that time it seems as if Smith and Wesson may have had substantial stocks of some parts that got stacked up somewhere and not used right away. My guess is that we still see the results of that over the last decade or so when they suddenly reintroduce some discontinued version for a small run.
I never talked to anyone who had to fire their gun who said "I wished I had the smaller gun and fewer rounds with me" Just because you find a hundred people who agree with you on the internet does not mean you're right.