Most people know exactly fourteen Bob Marley songs — the ones on the 1984 hits collection Legend, which has sold 10 million copies to date. This new twenty-track compilation shares eleven songs with Legend, dropping “Stir It Up,” “Redemption Song” and “Satisfy My Soul” in favor of tracks recorded before Marley was signed to Island, like “Soul Rebel” and “Trenchtown Rock.” It also includes the previously unreleased “Slogans,” thought to have been recorded by Marley in a Miami bedroom in 1979, with overdubbed guitar noodling by Eric Clapton. The vocal line echoes “Burnin’ and Lootin’ ” both melodically and in its exasperation with the status quo: “No more sweet talk from the pulpit/No more sweet talk from the hypocrites.” It still sounds urgent today. Not so for Black Eyed Pea Will.i.am’s chipper remix of “Africa Unite,” which drains the song of any resolve. “Stand Up Jamrock,” a stirring mash-up of “Get Up Stand Up” and son Damien’s “Welcome to Jamrock,” completes the disc. The new tunes make this a must for true fans, and while it’s impossible to condense so broad a career into one CD, the pre-Island sides make this the most well-rounded one-disc version of Marley’s music available.