“Every time I put the radio on, it’s ‘Oh My Lord,’” John Lennon said in December 1970. “I’m beginning to think there must be a God.” Lennon wasn’t alone. As his former bandmate George Harrison’s debut single blanketed the airwaves, a struggling New York publisher, Bright Tunes Music, must’ve heard divine intervention in the melody of “My Sweet Lord.” It was identical to a chestnut in their dusty catalog, “He’s So Fine.” On Feb. 10, 1971, as Harrison’s hit was idling down from four weeks at No. 1, Bright Tunes filed a copyright infringement suit. The older song, written...