Recent research shows that he went by the family name of Matsudaira while he was in Kofu (because use of Tokugawa was only allowed for those from the head family, the three privileged branches of the family, and the heir).
近年の研究では、甲府時代は松平を名乗っていた（宗家、御三家の当主、世嗣以外は徳川を名乗れなかった）。