This statement seemed contradictory but it was common description for some emperors; for example, Emperor Tenchi was enthroned in the 7th year of his reign and Empress Jito was enthroned in the 4th year of her reign.
一見して矛盾するが、この書き方は天智天皇、持統天皇のときも同じで、それぞれ治世の7年め、4年めに即位したと記す。