Farmed Yoshitatsu 10 times on NG+ and got several varied drops. Tokagemaru, Udoto, Barbarian's Hatchets, Genryu's Armor set and Merchant's armor set I remember for sure, as well as the katana skill book 'Dragon Fang' and the odachi skill book "Dragon Horn'. Farmed in the map "Point of no Return". Imagawa Yoshimoto dropped the White Bone Spirit Tonfas, Evil-Crusher Switchglaive, Master's Archer Bow, 'Punish the Proud' skill book for dual swords and the 'Windswept' skill book for switchglaive. The rest of the "Golden Boy" set is implied but I've yet to get the swords or armor. Farmed in "Imagawa Diehard". Obsidian Samurai drops Gozutenno's Axe, Starcutter Sword, and the Obsidian Samurai armor set so far, and Honda Tadakatsu drops the Tombokiri spear and Warrior of the East armor set. No luck with skills from either. Also obtained the wooden spear from the Dojo quest "Hanzo the Demon". Seems pretty evident looking at other replies that a number of items like corrupted weapons are shared across many drop pools and not specific to a single enemy / boss necessarily.