By the time Bob Dylan and the Band's The Basement Tapes came out on June 26, 1975, it was the most famous album never released. It was also one of the most frequently bootlegged.

The record had been written about, dissected, discussed and heralded as a masterpiece before Dylan's record company finally decided to put out some of the songs that were recorded by the singer and his onetime backing band eight years earlier.

Following a July 1966 motorcycle accident, Dylan retreated to his home in Woodstock, N.Y., to recover. He pretty much disappeared from public during this period, but in the summer of 1967, Rick Danko, Levon Helm, Garth Hudson, Richard Manuel and Robbie Robertson – who played together as the Hawks and backed Dylan in one form or another during his 1966 tour, and would later rename themselves the Band – began recording impromptu sessions with Dylan at his home.

Soon, they were meeting more regularly at the Band's house in nearby West Saugerties, N.Y., where they recorded many of Dylan's new songs on a basic reel-to-reel machine in the basement. Most of these compositions, which were sprinkled among the covers the group also playfully worked their way though, were to be passed on to Dylan's publishing company, which would then pair the songs with other artists (though Dylan initially balked at this commercial proposition, he eventually relented).

Nobody involved in the recordings that were laid down during the summer of 1967 expected anyone outside of a few industry executives, and perhaps a few potential clients, to hear the ragtag songs, which totaled more than 125 by the time the tapes stopped rolling. A 14-song demo tape was assembled by fall, and soon the sketchy, low-fi recordings were being passed around – at first among fellow artists and industry insiders. But word started to spread among Dylan fans, who hadn't heard anything new by the singer since Blonde on Blonde was released in May 1966.

By the middle of 1969, a bootleg album – rock's first – called Great White Wonder found its way into record stores. In addition to other Dylan rarities, including some recordings he made before he released his debut album in 1962, were seven songs from the Woodstock sessions.

The cat was now out of the bag. It didn't take long for word to spread that the handful of cuts on the bootleg was a small fraction of the material that was actually recorded.

Listen to the Band's 'Long Distance Operator'

And so began The Basement Tapes' long odyssey to legality. It was tricky. For one thing, the Band were signed to a different label. For another, Dylan wasn't interested in releasing a bunch of songs that he had no intention of releasing in the first place. But by early 1975, shortly after the release of Blood on the Tracks, Dylan's best album since his mid-'60s peak, he approved an official release of the recordings.

Even though the 24 songs that wound up on the double album represented a tiny portion of the tracks recorded during the three or so months Dylan and the Band were holed up in that New York basement, fans were generally pleased with the results. Several of the songs ("Tears of Rage," "You Ain't Goin' Nowhere," "This Wheel's on Fire") had long been available in other forms – either re-recorded by Dylan, the Band or other artists – but their inclusion here in their most primitive states, in some ways, makes them the definitive versions.

Still, the project wasn't without its critics, many of whom complained about the post-production tweaking of the original two-channel stereo recordings that were mixed down to mono. Plus, it didn't take long for fans to figure out that some of the songs included new overdubs by the Band, as well as tracks that were recently recorded by the group and were being passed off as vintage recordings.

Nevertheless, The Basement Tapes was a revelation, chronicling a previously lost period in the history of one of rock's biggest and most influential artists. It made it to No. 7, marking the Band's first Top 10 showing with a studio LP since 1970's Stage Fright (a pair of live albums, including one with Dylan, and another Dylan collaboration, 1974's Planet Waves, also reached the Top 10). Pieces were missing, but it's a monumental recording, either way.

Or at least it was. Over the years, bootleggers, once again, started assembling the original 1967 recordings – this time collecting almost everything they knew was out there. Once again, The Basement Tapes became one of rock's Holy Grails.

In 2014, almost 50 years after they were recorded, all 138 songs were finally released on the six-disc box The Basement Tapes Complete: The Bootleg Series Vol. 11, rendering the 1975 album obsolete. It’s an exhaustive and oftentimes exhausting collection. But it’s also a fascinating and historically significant document of one of rock’s most momentous summits whose legend is finally complete.