Although Genka reki was older than Giho reki, the new calendar was adopted for the older age and old calendar was adopted for the new age in "Nihonshoki."
元嘉暦が古く、暦が新しいにもかかわらず、『日本書紀』は、新しい暦を古い時代に、古い暦を新しい時代に採用している。