Back then there was no sophisticated, statistical analysis in determining #1 from anything. It was entirely subjected to opinions of those in newspapers and some coaches that would share an opinion. That carried into the tourney as well in who played who and where most likley influenced in what would bring the NCAA more money.
Still, I think it was STeve Green that went 10/12 or maybe 12/14 along the baseline for whatever margin that was in 75, which knight thought was his best team ever...that didn't win the crapshoot. Of all the good teams Knight had he always claimed his 75 team was the best and so the best team under knight for whatever reasons didn't win, telling the world that winning is a crapshoot in which a good team for a game or so is needed to win, but what would be considered a great team may not.
In 76 IU beat Purdue twice by an average of 3.5 points I seem to recall. One of those took place at Mackey where Purdue was in a position to put the game away and Buckner (foul or not?) took the ball away from Parkinson in the last minute or so. We are talking a bad call, an off knight, one less turnover???? Very little distinguished the difference between that team and the Purdue team rarely mentioned...other than IU did well in that couple of week stretch against those teams chosen by some reason.
Storming the floor probably has as much to do with Purdue losing the game whether number 1 or not. It was a great accomplishment for IU. However unlike Kentucky that refused to go to THAT PLACE and play but was willing to play elsewhere, Purdue will continue to go to that place and play as they have done for many years.