If you try to set the clock in Lisa OS 3.1 to 2010, you’re out of luck:
You can only enter years from 1981 to 1995. That’s a span of 15 years – why? And what happens if the clock runs past the end of 1995?
Well, it wraps around to 1 Jan 1980.
But why does it not allow entering 1980 then? That’s why:
Whenever the clock is set to 1980, it thinks the clock is not set up properly. So it is a 4 bit counter. Too bad, a 5 bit counter could have made it into 2011, and we all know that’s way more than ever needed.