What is Oosuriage in Japanese Katana terminology?

The term "Oosuriage/Oosuriage Nakago" (大磨上げ／大摺上げ茎, おおすりあげ／おおすりあげなかご) refers to a significant shortening of the overall length of a Japanese sword by greatly trimming the tang end (Nakagojiri). This process is done to such an extent that all inscriptions (Mei) and file marks (Yasurime) are removed, rendering the sword completely unsigned (Mumei). This term is used to describe a specific method of altering the length of a Japanese sword, which can significantly affect its historical and cultural value. Despite the loss of original inscriptions and file marks, this process does not necessarily diminish the sword's value, as other factors such as the era, provenance, and the presence of appraisal documents (Origami) are also taken into consideration in the evaluation of a sword's worth.