From a development viewpoint the double, with ejectors was perfected anywhere from 1880-1890. After that improvements have been minor and even debatable at best. The double was done by the end WWI. Vets saw the potential of repeaters and bought more A5, Model 12, 17, 37’s(17’s by another mother) and later 500’s and 1100’. We went from labor intensive guns to machine intensive made guns which went from two to five shells. Rarely does old increase much in value when it goes out of fashion.