The best answer would come from the shop. However, my recollection is the oval stamp bows were made by Sam back in the '50's. "Registered" bows were made by Sam beginning at some later date (I don't know when) up till the time of his death. I don't remember where the Kolstein & Son bows fit into the picture, but one of my bows was a bow in progress when Sam died and was finished a short time later. The stamp is different. "S. Kolstein & Son, N.Y.", if memory serves.