Calendars are a big deal in Japan (a trip to a stationary store in Tokyo will show this). New Year is the most celebrated holiday in Japan and anyone without a calendar is rushing to get one before January.
But the Emperor’s abdication presents a new issue for calendar makers and for the dating system as a whole. The Japanese calendar follows the Gregorian calendar structurally — starting in January and running to December — but the year is identified by the incumbent emperor and resets at year “1” at every imperial era.
So in 2019 the Heisei era will end and Japan will need a new name by which to identify dates. But no one knows what it will be called yet.
Calendar publishers face a difficulty in not knowing what to call the new era. There might not be enough time to design and publish calendars in time for 2019. While the new era is 12 months away, calendars can go on sale as soon as September — so in reality they only have a few months to firm up details and act accordingly.
Japan being a largely print society, the same can be said about things like notebooks and day planners (which are still consumed in paper form more than electronic).