Three-inch shells have been around just about as long as cartridge shotguns have been around. In my 1903 UMC catalogue there were 12-gauge paper shells 2 5/8, 2 3/4, 2 7/8, 3 and 3 1/4 inch. The 16-gauge was available 2 9/16, 2 3/4, 2 7/8, and 3 inch. The 20-gauge was offered in 2 1/2, 2 3/4, 2 7/8, and 3 inch. In those days the "standard" 2 5/8 inch 12-gauge, 2 9/16 inch 16-gauge and 2 1/2 inch 20-gauge shells carried a slightly milder maximum load than the 2 3/4 inch and longer shells. The advantage of the 2 7/8, 3 and 3 1/4 inch shells was more and better wadding for a better gas seal which many serious Pigeon shooters thought to be an advantage.
All the manufacturers would chamber new guns for the longer shells upon request, but the chance of that is pretty remote in a Field Grade. These earleir guns for long shells were seldom, if ever, marked as to chamber length. I guess in the old days shooters were just smarter, and knew what length shell their guns were made for.
The "Chambers 3 Inches" marking seems to have begun with the introduction of the 12-gauge 3-inch shell loaded with a maximum charge of progressive burning smokeless powder and 1 3/8 ounces of shot in the 1920s. Western Cartridge Co.'s Super-X load leading the progressive burning powder revolution.