I was thinking this exactly. Not much of a problem for data, more of a problem for display of the data. A good stop-gap until they get enough information about the new era would be to just display the dates in UTC for a while or something.
I mean, unless they're storing the date/time in the database as a string, formatted for Japan's locale. Then they're screwed, kind of. I mean even then, it could be fixed with a stored procedure within an update statement.
As much as using UTC would be better, I suppose for many that will not be an option if they are accustomed to Japanese dates. I mean, I got flak in work because I was writing dates (as in, written on printed paper) in the ISO-8601 format and apparently the administration in France does not understand that.
There are all kinds of random places where this has potential to show up. For example, some backend process breaking (or worse, silently discarding data) because of validating dates in incoming data from another system as a string regex that expects the old era symbol.
I mean, unless they're storing the date/time in the database as a string, formatted for Japan's locale. Then they're screwed, kind of. I mean even then, it could be fixed with a stored procedure within an update statement.