In the old Imperial Family Law, the principle of male-line succession was established as a written law, and the current Imperial Family Law also followed it; the official interpretation of it by the government doesn't exist before/after War.
旧皇室典範がはじめて男系の継承原理を成文法とし、現在の皇室典範もこれを踏襲したが、戦前も戦後も政府としての公式解釈は存在していない。