As we neared the new millennium back in the 90s, we realized there were two ways to solve the looming Y2K problem. One was to expand the “year” fields in databases to have 4 digits instead of two. That would postpone the problem until the year 10000. Another way was to leave the fields in the databases as 2 digits and throw in some logic to decide which century it belongs to. You could, for example, say: IF year IS GREATER THAN 80 THEN century = “19” ELSE century = “20”. That would have solved the problem until the year 2080. The arbitrary value of 80 is what some people call the “pivot year.”
Except some people decided the pivot year would be 20, and guess what? Systems started failing last week. Back in the 90s, a lot of people would have probably said that the program wouldn’t still be in use in twenty years, and still others likely said they themselves wouldn’t be.
The Y2K.2 problem is not as severe as Y2K because there are far fewer instances, and also you can just punt the pivot year ahead another 20 years, which would be an easy fix (assuming you can find the source code).
Some programs store the year in full 4 digits, but allow a 2-digit shortcut. That is what Excel does. I just tested it out and on my computer their pivot year is 30. If you enter 29/12/31 it converts it to 2029/12/31. If you enter 30/1/1 it converts it to 1930/1/1. I just did a bit of research, and there is a default two-digit year range that you can set in the Windows Control Panel (Regional Settings). There you can set the pivot year to whatever you want.