I've been cuckoo for Disney lately (moreso than usual at least
), and have looked up several Disney fan sites. One of them said that a lot of Disney fans don't consider the 17th to be the anniversary date, but the 18th instead.
I guess Disneyland was only opened to "invited guests" on the 17th, and to the public on the next day.
So there's a little trivia for you, and maybe you guys were there on the actual anniversary!