If there’s a positive quality uniting the great-to-horrible expanse of Stephen Stills’ collected songbook, it’s probably that Stillsa Dallas-born Southern man who moved to New York after he dropped out of collegeis as unapologetic as they come. That quality has led to some astoundingly good work: There’s his moment-defining guitar on Buffalo Springfield’s “For What It’s Worth,” and the folk-solidarity plea he’s making. And on “Love the One You’re With”his biggest non-CSNY song, as well as the lead cut and single from his solo debuthe recruited none other than bandmates David Crosby and Graham Nash to sing back-up. Stills has gall.

But that doesn’t always translate into great songs. Consider what may be Stills’ worst song ever, “Dark Coral,” from his 1976 album with the Stills-Young Band. Above an insipid light-soul backdrop, he puts both Plato’s cave and heaven at the bottom of the ocean, memorializing, “The deeper you go/ Cause of the pressure of the air/ Nitrogen comes and goes/ And gets you high.” Songs like that require commitment, surely, but they’re not indicative of the best filter.

This isn’t new. On April 26, 1968, Stills was recording a session with Judy Collins. When she was done, he rented the studio for an hour, let the tape roll and walked away with a full tape of the songs he’d written for both the Crosby, Stills & Nash debut and his solo debut. Stills later lost the demo. A decade later, someone found the two-reel master of that session in a dumpster outside of the California studio and held it for almost 30 years. Last year, Nash delivered it to Stills, digitized and ready for release.

“It’s just me and my guitar or piano, and it’s called Just Roll Tape. Some of it didn’t quite make the cut because it wasn’t English or even notes,” says Stills, who will release the collection in May. “But I did as little cherry-picking as I could. I dropped three different false starts.”

Stills, now 62, admits that he doesn’t sound quite like he’s 23, anymore. (“Wow, my voice was high. I can still get up there, but not quite that much.”) And when he sings, he’ll be staring at an Apple laptop, checking the lyrics he may remember against a database of 40 songs.

“Everybody get ready. When you hit 60, you’ll run into these kinds of problems,” he says. “We had them on the last CSNY tour, and I went, ‘Oh my god, this is heaven.’ I basically said, ‘Well, I ain’t proud, I’m going to do that!’”

Stephen Stills plays The Lincoln Theatre Monday, April 23, at 8 p.m. Tickets are $35-$50.