They predicted darkness and martial law. Didn't even flicker. The phones and communications satellites, which also faced a brick-wall deadline, kept working. So did the water utilities. So did the air traffic control system.
All software has bugs.
The vast majority are benign annoyances which can easily be worked around. Folks, don't think for a moment that all Y2K bugs were fixed by midnight yesterday, not even in the aforementioned utilities. Good enough will do, and this forum is actually a great example of that. The only harm done is that the years look ugly. Because they were listening to the wrong people.