“I suspect. Duke has been a top 10 school in the USNWR rankings every year since 1985 with only one exception (#12 in 1989).”
Actually the very first ranking was in 1983 and set the perception for applications in the early to mid-80s, had Duke unranked and Dartmouth 10th. So at least then the perception was that Dartmouth was a a little better than Duke.