Well, to be fair to Apple, in the mid-eighties, the turn of the Millennium seemed like an eternity away.
In 1983, I remember George Lucas saying that the next Star Wars movie wouldn't be out until 1997 and thinking how far away that was. The year 2000 (1) was even further away.
I think that the idea that people would be using Macs made in the 1980s after 2019 was just bizarre. These were days of great advances in processor speed, RAM, GUIs for computing in general. Machines doubled in speed, power and potential every couple of years. Would you buy a machine now that couldn't rendered dates after 2100 correctly?
Weekday-month-day-combinations repeat themselves every 28 years, if I am not mistaken. Century years not divisable by 400 mess this up a bit though. I'll be setting my year back to 1992 in my System 6 installations when the year 2020 rolls around unless I find an INIT that allows 2020 (and there surely is an INIT for that).
(1) The turn of the Millennium was either at the beginning or the end of the year 2000, depending on how difficult or contrary you are. For me, it was the end of that year. That being said, I didn't complain when the city I was living in celebrated the beginning of that year.