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davidcyclebackOrdinarilly, a cabinet card will have a real photo (no dots) image. But there are genuine vintage cabinet cards that have photomechanical prints instead of photos. For example, those oversized 'Horner Cabinets' of MLB players have photomechanical prints. Usually, cabinets with photomechanical prints were distributed commercially and will have popular subjects, like Buffalo Bill and Sitting Bull. A star baseball player would quality as a popular subject.
I can assure that the mount itself is from the correct period.