Written in Their Soul collects 140 previously unreleased demos from Stax Records, the Memphis label whose 1960s and ’70s stars included Otis Redding, the Staple Singers, Isaac Hayes, Sam and Dave, Carla Thomas, Rufus Thomas and Eddie Floyd. Released on June 23, the set ranges from spare but soulful early versions of hits to fully-fleshed productions that were never released.

Available digitally and as a seven-CD box set, Written in Their Soul is divided into three categories: songs released by artists on Stax and its subsidiary labels; songs composed by Stax songwriters but released by other labels, such as Atlantic; and material that was never released anywhere. Robert Gordon, the author of Respect Yourself: The Stax Records Story, and Deanie Parker, the singer-songwriter who became Stax’s first director of publicity, wrote the liner notes.

Unusual for the 1960s, many Stax songwriters were women. In addition to Parker, they included singing star Carla Thomas and the prolific Bettye Crutcher. Represented by two dozen demos on Written in Their Soul, Crutcher composed hits for Johnnie Taylor and the Staple Singers.

Mack Rice’s hard-driving demo for the Staple Singers’ 1971 hit, “Respect Yourself,” is among the collection’s standouts. Rice and co-writer Luther Ingram found their initial inspiration for the soul anthem when one of them used the phrase “respect himself.” “It hit us both at the same time,” Rice said.

On disc one, William Bell’s demo for the regret-filled “What Did I Do Wrong” is heartfelt and full despite its minimal accompaniment. The same goes for Carla Thomas’ “Sweet Sensation” and the collection’s Eddie Floyd’s demos. Bell’s mournful “Slow Train,” reveals the natural connection between country music and Southern soul. Country flavor also informs the Staple Singers’ “Hear My Call, Here,” but the Staples’ “Top of the Mountain,” featuring the dynamic Mavis in the lead, showcases their signature gospel-soul sound.

“634-5789,” a Floyd demo, appears on disc four. Raw though it is, it’s the recipe for Wilson Pickett’s recording of “634-5789,” the singer’s second number one R&B hit. Disc four also features one demo sung by Delaney Bramlett, a future star with the duo Delaney and Bonnie, and several more Rice demos.

Never released songs sung by Floyd, William Bell, Rufus Thomas, Shirley Brown and others fill disc five through seven. With so much songwriting talent behind them, maybe such-shelved songs as Homer Banks’ “Grandpa’s Will,” Crutcher’s “The Yard Man” or Floyd’s “Hometown Lover,” to name a few, will have their day, too.