Empress Komyo' was not a shigo (posthumous title) or a posthumous title, but a common name, and her formal honorary title was 天平応真仁正皇太后 (Empress Dowager Tenpyo Oshinninsho).
なお、「光明皇后」というのは諡号や追号の類ではなく通称で、正式な尊号は天平応真仁正皇太后という。