Comment by 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.