In 2008, sojodome (the contents of petitions collected by close associate) was found from the documents of the head of the Tokugawa family in the survey conducted by the Tokugawa Memorial Foundation and is attracting attentions as an important material.
2008年、徳川記念財団の調査により徳川宗家文書から訴状留（側近が訴状内容をまとめたもの）が発見され貴重な資料として注目される。