Uh... it's not a "once in a century" event. Unless I'm mistaken there was one back in 08/08/08 which was 1 year, 1 month, and 1 day ago. Now the next one won't be for another 992 years on January 1, 3001. There's nine such events per millenium all in the first nine years of each millenium.
My bad... sort of. It's still not once in a century. It's 9 times a century. With it reoccuring 92 years from now in 2101. But still...
You're right. It has to do with three nines and some good luck attached. Lot of couples marry on the day. However, in China or somewhere it is considered bad luck.Next one will be 09/09/2109
We do have 10/10/10, 11/11/11 and 12/12/12.
SD, single digit. Those are double digit numbers.