This is one of many interesting Zeenut questions. Frank's 1-3% is very reasonable. In my opinion it is likely on the lower end, closer to 1%. In general you see more from 1924-1936 than the other years. This is not shocking, although for some reason 1915s with coupon appear to have survived more than the others from 1913-19. 1920 with coupon is very difficult to locate in my opinion.
Andrew
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