[thaumasiotes]

> This also means that, when an era changes, the Gregorian year will have two imperial year designations, for example 1989 is both Showa 64 and Heisei 1, depending whether the day of the year is before or after the imperial transition.

This isn't unusual. For example, the American calendar year 2024 belongs to both the school year "2023-2024" and the school year "2024-2025".

The general phenomenon here is "sometimes things begin when it isn't calendar New Year's Day", which is universal to all cultures.

[chirsz]

In ancient China, the imperial year designations were usually changed in the second year following the coronation of a new emperor, thus preventing the occurrence of two imperial year designations in the same year. Japan seems to have chosen to change the imperial year designation in the same year because of the faster flow of information in modern times. I still think it would be more convenient to change it the second year.

[kijin]

Japan has been using their unique system for over 1000 years. It's not a recent change. They never really cared for the Confucian standards of Chinese emperors. (If they did, they wouldn't have called their own monarch an emperor!)

I say Confucian standards, because the Chinese rule of changing the imperial year designation in the second year of a new emperor seems to have been more about propriety and respect for the late emperor than it was about convenience. A number of emperors actually changed the year designation immediately upon ascending to the throne, which was seen as an attempt to discredit their predecessor.

[juped]

No, the Japanese imperial calendar oddness is that it's otherwise exactly the Gregorian calendar, but the era may change midyear.