Howdy
Yes, it is a good question and there is no definitive answer.
With Colt it is easy. 1900 is the year that Colt first factory warrantied their revolvers to be safe to shoot with ammunition loaded with Smokeless powder. Colt had been steadily improving the quality of their steel and by 1900 felt confident that their revolvers could be fired with Smokeless powder.
Soon after 1900 Colt began marking the letters VP for Verified Proof in an upside down triangle on the left front side of the trigger guard to indicate their revolvers were safe to fire with Smokeless ammunition.
There is no reason to suspect that Colt had access to steel that was any better than Smith & Wesson could obtain, but here is a quote from a catalog from about 1900. "While we do not guarantee our Revolvers when used with smokeless powder, and strongly advise against reloaded ammunition, we do not wish to detract in any way from its merits or discourage the use of properly loaded smokeless cartridges."
By the catalog of 1905-1906 they had changed their tune slightly. "Cartridges in which smokeless powder is used are made by leading manufacturers, and they posses 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 ammunition, we have no desire to detract from its merits or discourage its use when properly handled".
So it sounds to me that by 1905 what S&W was saying was go ahead and use smokeless ammunition in our revolvers, but if it blows up we will not compensate you for it.