Based on historical documentation stating that Doton was Sadatsugu's nephew, some local historians point out that many other possibilities exist, such as the possibility that Sadatsugu's brother was adopted by the Nariyasu clan or that his sister married into the Nariyasu clan.
また、定次と道頓の関係を甥としている史料もあることから、定次の兄弟が成安氏に養子に入っていたか、姉妹が嫁いでいたなどいろいろな可能性を指摘する郷土史家もいる。