Note that a lot of that old code that caused so much of the fuss in Y2K wasn't ever supposed to be around even a decade after it was written... the phase change caused by IBM OS/360 and widespread backwards compatibility froze it in place.

Normally, you rewrote everything for the new system when it showed up, and used the knowledge gained from the old one to make the new one better. This suddenly stopped when you didn't need to do it, and everyone decided to save time/money and make due with the old code.