I’m attending a great short course on non-inferiority trials and the speaker provided a key reference of historical interest. This reference is the one that got the Statistics community interested in the concept of non-inferiority. The full text is behind a paywall, but you can look at the abstract. A footnote is a paper, Dunnett and Gent 1977, (also trapped behind a paywall) addressed this problem earlier.
Blackwelder WC. “Proving the null hypothesis” in clinical trials. Control Clin Trials. 1982 Dec;3(4):345-53. Article is bheind a pay wall.