I have Model 1899 serial number 225 - lettered as having been shipped in December 1899. The barrel is unmarked, but the cylinder chambers .38 Special cartridges. I regularly shoot it with light smokeless powder reloads, so I guess I've voided the warranty!

As to when S&W first approved their guns for smokeless powder, I've heard 1909. This would be supported by the fact that the .44 Special was originally a black powder cartridge and it was introduced in the Triple Lock in 1908. Perhaps Roy Jinks could weigh in on this.