This appeared at first to be the same as the 1933 Senator, but is dated 1931 and has 17 jewels as opposed to 15J for the others. When I looked more carefully I saw that the case above the 12 and below the 6 is beveled flat not rounded like the Senator. And when I looked even more carefully the stepping continues in the lugs.
I entered the inside case number in the form. The outside case number is 218271. Is it common for inside and outside case numbers to be different? Is there a reason for two different numbers?