The 4,000 year rule has been proposed by some writers but it is not part of Pope Gregory’s system nor has any official body I know of accepted it.
It certainly wasn’t part of the Pope’s system, but I did find it in the Encyclopedia’s description of the calendar.
I’m not going to stay up nights worrying about it. I’m just disappointed that 2000 WILL be a leapyear, I thought it was so cool that most century years AREN’T.
CK: you’re disappointed? Heck, I’m pissed! Because February of 2000 AD will have 29 days, the Navy gets an extra day out of me before retirement.