The top 10 (11) are very stable.

Other schools, Northwestern, Cornell, Brown and Washington U made into the (tied) top 10 once or twice in the history of the rankings.

But the above 11 schools are quite stable, except that U Chicago didn't make the top 10 for 7 times from 1999-2015.
Columbia was out for 1 time, and Dartmouth was out 5 times.