Someone can correct me if I am wrong, but it is my understanding on a combat masterpiece that model numbering started while they were still making 5 screw guns, ( the model number then being 15) and when they deleted the screw in front of the trigger guard it became the 15-1. However I have a non model marked combat masterpiece with a 4 screw frame. So during those transition periods things can get very mixed up.
For some less popular models, it would not be unheard of for a non model marked frame to be use$ assembled and shipped without a model number well into the 1960's
For some less popular models, it would not be unheard of for a non model marked frame to be use$ assembled and shipped without a model number well into the 1960's