Documentary maker Morgan Neville trains a spotlight on the little-known world of rock and pop backup singers, those anonymous, hard-working women (and, occasionally, men) who support stadium megastars like David Bowie, Bruce Springsteen, and the Rolling Stones. The movie takes its cues from Standing in the Shadows of Motown (2002), another act of pop-culture revisionism that tried to give musical credit where it was due, and the story begins in the early 60s, with the effervescent Darlene Love cutting “He’s a Rebel” for producer Phil Spector and then seeing him credit the single to another act, the Crystals. The machinations of Ike Turner, who recruited and commanded the various Ikettes, come in for further censure, though Neville also concedes that when some of these performers have tried to launch solo careers, they haven’t gotten anywhere. Among the singers profiled are Claudia Lennear, whose star-studded resumé includes gigs with Joe Cocker, Leon Russell, and George Harrison, and Merry Clayton, who upstaged Mick Jagger on the studio recording of “Gimme Shelter.”