Serialling on large-size notes was a bit irregular. As the volume of currency in circulation increased, the Treasury had to keep inventing new systems to keep from running out of serial numbers. The 1899 $1 was, by far, the longest series up to that time, so it went through several of these variations.... The first block of 100,000,000 notes were like the one you've got: plain numbers, with no letters at all. The next fourteen blocks had a letter prefix but retained the symbol suffix. The abbreviated alphabet was A, B, D, E, H, K, M, N, R, T, V, X, Y, Z. The next fifteen blocks had matching prefix and suffix letters. These blocks were AA, BB, DD, EE, HH, KK, MM, NN, RR, TT, UU, VV, XX, YY, ZZ, using almost the same alphabet as before except for the addition of U. Then the last eleven blocks used non-matching letters, with a prefix advancing through the alphabet while the suffix stayed stuck on A. So the blocks were BA, DA, EA, HA, KA, MA, NA, RA, TA, VA, XA (and note that U was omitted this time around). Picking up (more or less) where these left off, the 1923 $1's then used thirteen blocks with suffix B, thirteen with suffix D, and finally AE and BE. At that point, the block system had developed into something like what we're used to on small-size notes: the suffix letter only changes after the prefix letter makes a complete round through the alphabet. The innovation in the serialling of the small-size notes was the use of an almost-complete 25-letter alphabet (omitting only O) instead of the abbreviated alphabets that had been used for large-size serialling. On that system, the 1935-series $1's used blocks AA through EJ, a total of 235 blocks!
Yeah, looks weird to me and I couldn't find anything about it online or in the books I have. I'm thinking maybe some knowledgeable collectors here can tell me more.
Serialling on large-size notes was a bit irregular. As the volume of currency in circulation increased, the Treasury had to keep inventing new systems to keep from running out of serial numbers. The 1899 $1 was, by far, the longest series up to that time, so it went through several of these variations.... The first block of 100,000,000 notes were like the one you've got: plain numbers, with no letters at all. The next fourteen blocks had a letter prefix but retained the symbol suffix. The abbreviated alphabet was A, B, D, E, H, K, M, N, R, T, V, X, Y, Z. The next fifteen blocks had matching prefix and suffix letters. These blocks were AA, BB, DD, EE, HH, KK, MM, NN, RR, TT, UU, VV, XX, YY, ZZ, using almost the same alphabet as before except for the addition of U. Then the last eleven blocks used non-matching letters, with a prefix advancing through the alphabet while the suffix stayed stuck on A. So the blocks were BA, DA, EA, HA, KA, MA, NA, RA, TA, VA, XA (and note that U was omitted this time around). Picking up (more or less) where these left off, the 1923 $1's then used thirteen blocks with suffix B, thirteen with suffix D, and finally AE and BE. At that point, the block system had developed into something like what we're used to on small-size notes: the suffix letter only changes after the prefix letter makes a complete round through the alphabet. The innovation in the serialling of the small-size notes was the use of an almost-complete 25-letter alphabet (omitting only O) instead of the abbreviated alphabets that had been used for large-size serialling. On that system, the 1935-series $1's used blocks AA through EJ, a total of 235 blocks!
Thank you @Numbers. I read the OP’s question and referenced your website, but didn’t understand what I was looking at until I read your explanation. http://www.uspapermoney.info/serials/s1899_s.html
I did look at the site you mentioned but I couldn't find the link to navigate to 1899. Thanks for the link!