Good news on this specific issue: the current year will be both the final year of the old era and the 元年 (first year) of the new one. The following calendar year is the 2nd of the new era. So in most cases you have a window of time to get ready to update systems to accommodate e.g. Japanese counterparties whose systems want you to specify dates of birth using eras in preference to the Western calendar.
One of the relatively few bits of ultimately consequential engineering I did in the last few years was assisting a colleague in grepping for comments we had both left identifying code to update in the event of a new era. (We are currently, of course, in Reiwa 6, and Heisei ended in what most HNers consider 2019.)
One of the relatively few bits of ultimately consequential engineering I did in the last few years was assisting a colleague in grepping for comments we had both left identifying code to update in the event of a new era. (We are currently, of course, in Reiwa 6, and Heisei ended in what most HNers consider 2019.)