However, why the Tairo post had to be solely occupied by the members of the four families is not thoroughly clear, for example, descendents of Tadatsugu SAKAI, of Yasumasa SAKAKIBARA, and of Tadakatsu HONDA, who were important Fudai daimyo and called Tokugawa-shitenno (four generals of the Tokugawa clan) surpassing the Hotta family even in the amount of rice crop, were not appointed the post.
しかし、徳川四天王と称せられ、石高でも堀田家を上回っていた譜代重鎮の酒井忠次・榊原康政・本多忠勝の末裔はこれに任じられないなど、大老四家を固定した基準はいまひとつ不明である。