I'm not sure of the actual dates, but I'm pretty sure that Colt started warranting their Peacemaker revolver as being suitable for smokless loads starting around 1898 or 1899.
Smith & Wesson hand ejector revolvers were being designed right in the heart of the transition from black to smokeless. I'm not at all sure of the hows and whys of their design and suitability for use with smokeless, but I've never seen anything saying that even the earliest Hand Ejector, the Model of 1896, isn't suitable for use with smokeless.
Colt Single Action Army cylinders and frames were made of malleable iron starting in 1873. Although Colt had been making frames and cylinders from various types of steel as early as mid 1883, they did not factory warranty the Single Action Army for Smokeless powder until 1900 because of improvements in the heat treating of cylinders.
I'm pretty sure it was 1901 that Colt began putting a V/P in an upside down triangle on the trigger guard that stood for Verified Proof, signifying at a glance the revolver was factory warrantied for Smokeless Powder.
Smith and Wesson is harder to pin down.
I have searched high and low but I can fine no authoritative source on when S&W felt it was safe to fire Smokeless powder in their revolvers.
I have a reprint of a 1900 S&W catalog, and S&W is warning against shooting Smokeless powder in their revolvers in that catalog.
Smith and Wesson developed the 38 Special cartridge in 1899, and at the time it was loaded with Black Powder.
Here is a page from the 1900 S&W catalog regarding the new 38 Special cartridge.
This is the 38 Military and Police (Model of 1899) cataloged in 1900. S&W would not be factory warrantying this revolver for Smokeless Powder at this time. This revolver eventually became known as the Model 10 in 1957.
The 1905/1906 catalog is ambiguous. regarding the use of cartridges loaded with Smokeless powder. In it S&W cautions against the use of reloaded ammunition made with Smokeless powder, citing their view that the quality of the powder ammunition loaded with Smokeless powder may be questionable.
Quote:"Cartridges in which Smokeless powder is used are made by leading manufacturers, and they possess valuable qualities not found in Black Powder ammunition. They do excellent work in our revolvers,
and while we do not guarantee our arms when Smokeless powder is used, and strongly advise against reloaded Smokeless ammunition, we have no desire to detract from its merits or discourage its use when properly handled"
Note: the Italics are mine.
So S&W was hedging their bets, not wanting to take responsibility if somebody blew up one of their revolvers with ammunition loaded with Smokeless powder.
Practically speaking, I don't believe Colt had access to better steel than S&W did about 25 miles up the Connecticut River, but S&W seemed to be hesitant to guarantee their revolvers for Smokeless powder.
The 44 Special cartridge was developed by S&W in 1907, originally loaded with Black Powder. When the Triple Lock was introduced in 1908, it was the first revolver chambered for the 44 Special cartridge, and by that time I have found no mention that the Triple Lock should not be fired with Smokeless ammunition, and the same for the 38 Military and Police.