What ranked team did we beat in 1974? We had two wins that year, the most impressive over the Pacific Coast Athletic Conference's San Diego State Aztecs.
If you mistyped, and are referring to the oh-so-referenced Tennessee game in 1975, The Volunteers had a disappointing 5 loss season with no bowl bid, at at the time NT defeated them, they had already dropped 2 of the previous 4 games and were not ranked in the AP poll (they would finish the season unranked as well).
And assuming you were referring to the Tennessee game per usual, the 1975 NT team did not win a single other game over a team with a winning record that entire season - other wins came against the likes of Drake, WTAMU, Cal Poly-Pomona, and UTA (all which had losing records, even at their low level of competition).
To hold that team and that win up as the gold standard of NT football is fallacy, especially in light of accomplishments made since the mid-70's. I hope we get "back" to far more than that.