sashikomi/hadori
I aim these comments primarily at newer collectors.
From "New Gen. of Jap. S/smiths" by Tamio Tsuchiko p.216 and 218 hadori is "whitening inside the hamon and drawing the hamon line" and the accepted originator of this type of polish was one of the surviving lines of the Hon'ami after the Haitorei into about 1930s. Nakahara pp.83-85 discusses this hadori and describes sashikomi as a polish that brings out "all the blades features" and follows the true hamon line.
Broken down to its simples
Nitric acid treatment is just a tip of iceberg.
There is hundreds of treatment as well as neutralizing treatment which are almost all secret by each school and each polisher. (maybe some are good, some are not)
and Meiji Period is that Japan's industrial revolution, so, after Meiji period those study developed a lot.
They (all craftsmen) are constantly researching and developing new idea, we never know what they know today.
I believe that they were doing all the time with what they have in E