Since the Crown Prince had actual political control of the Japanese Shosei, it was different from the one in China where the Empress or the Empress Dowager used to take control of politics, it is presumed that above case was formally called 'Shosei' as the Empress Dowager (Emperor Saimei) was first appointed the nominal highest position followed by former Emperor's Empress (Emperor Kotoku's Empress, Princess Hashihito).
先帝の后や母后ではなく皇太子の方が実権を握っている点で、中国の称制とは異なるが、まず母后（斉明天皇）のちに先帝の后（孝徳天皇の皇后・間人皇女）を名目上の上位者として立てていたために形式上「称制」という名称が選ばれたのであろう。