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The NBTHK is one of the largest organizations dedicated to Japanese swords. Their origami, or authentication papers, are held in very high regard. There are four levels of papers currently issued by the NBTHK: Hozon, Tokubetsu Hozon, Juyo, and Tokubetsu Juyo.
Juyo papers are especially rare:
As of 2014, there are:
14 Muramasa katana,
and 7 Yari. (Which is incredible, as it is almost impossible to get a yari through Juyo)
Credit: D Brockbank