My SN book has numbers starting at 1920 also. I also noticed 1920 was 11000, 1922 was 11500, 1925 was 12000, so you interpolate approx. age. I had one back in the 1970's that looked like the one in the photo, Bullard was still in business then, when I call them I was told it was built in 1910. When I remarked wow, that old!! I was told it wasn't broken in yet. I found he was right!! Sometime later I was in a very large shop in Patterson NJ. They had an older one they were still using that they used to make Steam Engine Wheels back during the Civil War.