There is a view that Tsunakatsu died suddenly because Yoshihisa poisoned him, but this is considered a groundless rumor spread by Hachiya FUKUOJI, a feudal retainer of the Yonezawa domain, who lost his position in conflict with Hyobu CHISAKA, Edo-garo (one of the highest-ranking vassals of a daimyo during the Edo period) of the Uesugi family.
綱勝急死は義央による毒殺説が存在するが、これは上杉家江戸家老千坂兵部らと対立して失脚した米沢藩士福王子八弥の流言飛語で、信憑性は乏しいとされている。