To be fair - it was your clue that did it. I couldn't for the life of me work out what the answer was - I was thinking solar eclipses, blue moons, the date of Easter - you name it, I considered it.
Then I did a search here on KB for any other posts you'd made about university and discovered the one you attended. (No, you're not sensitive about it,
at all!)
I googled that to discover the year it was founded which made it easy to see what the years had in common and why no other years before 2000 could fit the bill.
Interesting little mystery!