An incredible debut, released 50 years ago [[11-6-71). I still have my copy! According to Wikipedia, though ... we've probably discussed this before -

Group members Airrion Love, Herb Murrell, James Dunn, and James Smith can be heard on "You're a Big Girl Now," recorded and released as a single prior to the beginning of production on the album, but according to lead singer Russell Thompkins Jr., they're absent from the album's other eight songs aside from Love's harmony vocals on "You Are Everything."[6] In John A. Jackson's book A House on Fire: The Rise and Fall of Philadelphia Soul [[2004), Sigma Sound Studios founder and engineer Joe Tarsia says, "I don't care if it was the Stylistics or Harold Melvin and the Blue Notes, or whoever. All the backgrounds on all those songs were sung not by the groups, but by either Kenny Gamble, Leon Huff, Thom Bell, Carl Helm [or] Bunny Sigler," while Sigler says that "most" of the male background vocals on the Stylistics' hit songs were provided by himself, Gamble,Bell and Helm.