Well, Luke, I cannot say I've made a statistically accurate survey of Sumi! Just something I've read in an old Japanese mag. It does seem to me that there is a tendency for Sumi to mature earlier along the backbone just past the dorsal fin, or along the base of the dorsal fin.
At Koi America there were 3 Shiro Utsuri that I spent a` lot of time comparing. One was a Matsunosuke-bred in the high-priced Quality Koi tank. One was the "dealer winner" in Ray Abell's tank ... a 7 (!)year-old. And the 3rd was the Grand Champ B owned by Art Lembke. The Lembke Shiro was the one described as having "country sumi" by the head judge. I thought the 3 made a great comparison. The quality of the Sumi on the ones for sale was superior to that of the Grand Champ B, but it had greater size, superior shape and a lot of "presence"... enhanced by a fine pattern. (If someone had bought the two Shiros in the dealer tanks and entered them in the show, would the result have been the same? ..... I think so. The Lembke Shiro is a grand fish. The other two have a lot of development to do to reach the same overall physical impression.) Nonetheless, the Sumi on those was so thick that I kept going back to them to try to distinguish the pigment. I could not decide if one was better than other as far as the Sumi went, because I was unsure how far along the two fish were in their development. The Abell Shiro had Omosako type blocks of pattern that were not filled-in completely. Would they ever come together? Many Omosako Shiros seem to never finish forming their pattern, giving a certain sloppiness to the overall look. The Matsunosuke-bred Shiro, on the other hand, had a pattern I loved ... lots of veins of Sumi, but the fish showed signs of a little stress, and the gloss of the Sumi was not quite as high as on the Omosako-type. Both were wonderful fish anyone would be proud to own. I kept asking myself which had the better Sumi. On that weekend, the one looked better, but I kept thinking that if the other had not been stressed by the far longer trip, it may have been better. Not that I was in the market for any fish in the price range of those two, but I could not decide which of the two I would want to buy, if either ... because I had no confidence in predicting the future of either. I could imagine either one finishing to be a grand dame of koidom, but I could not say it was anything more than my imagination.
Some day I would like to be able to observe such fish and make a considered judgment and have it prove true when the fish matured. .....Of course, with my ever fading eyesight, maybe it is just as well to have an active imagination.