Press embargoes are silly and square, doubly so when the content is music that has been widely circulated for over 40 years and would have continued to find new audiences without any external help. Since Bob Dylan’s 1967 home recordings began to leak two summers later, The Basement Tapes have been a secret that nobody could keep, and as of last week, constitute a six-CD, 139-song collection that anybody can buy.

The 11th entry in Dylan’s ongoing Bootleg Series, The Basement Tapes Complete sets out to resolve the central mystery of the murky songs first issued on Trademark of Quality’s Great White Wonder 1969 bootleg LP, bowdlerized by Robbie Robertson for 1975’s still-transcendent The Basement Tapes double album, and coming out in bits and pieces ever since. Adding some two dozen never-leaked songs to the Basement canon, the Complete version offers cleaned-up sound quality that should trigger nothing but ecstasy in the heart of any Dylan fan. But even as the music itself has become immeasurably more complex, with heretofore unheard harmonies and rich arrangements, sequenced chronologically and paired with historically clarifying liner notes, the set also offers a valuable reminder that knowing secrets and understanding secrets are very different things.

When Bob Dylan and members of his backing band, The Hawks, began to record in various above-ground locations around Woodstock in early 1967, they’d been off the road for less than a year. Intending to create songwriting demos for other musicians to arrange and cover (and generate income for Dylan), the nearly 12-dozen songs they recorded over the next year sounded nothing like the music they made together before or would play together later. Less a lost album than a body of work by itself, the Tapes comprise folk ballads, country croons, rock stomps, R&B grooves, answer songs, novelty songs, ominous songs, sad songs, wise songs, sweet songs, and weird songs. Dylan wrote many, remembered others, and — in a lot of cases — did something between the two. Greil Marcus’ 1997 book, The Old, Weird America, maps The Basement Tapes to the “invisible republic” of the Anthology of American Folk Music, the sweeping six-LP set compiled by the avant-garde filmmaker/alchemist Harry Smith (itself a kind of lore-filled bootleg). Todd Haynes’ misunderstood not-a-biopic on Dylan, 2007’s I’m Not There, envisions the album’s world as a surreal antediluvian backwater dreamed by a willful amnesiac. While both remain valuable portals into Dylan’s music, The Basement Tapes Complete reveals that, truly, the songs map to nothing but themselves.

Most frequently, The Basement Tapes contains inscrutable songs, maybe the most inscrutable of Dylan’s career. Borrowed by Haynes for the title of his film, the breathtaking “I’m Not There” — an elliptical, lovelorn sequel to “Sad-Eyed of the Low-lands” — verges on actual syntactical collapse. Existing only in one take, the words mostly do not actually make sense, and not merely in an obtuse, artful way. Technically, it is an unfinished composition, improvised lyrics filling in melodic gaps, but the result is a kind of speaking-in-tongues magic supported by a sparkling organ/piano weave by Garth Hudson and Richard Manuel. Here and everywhere, underscored by the newest remix, The Basement Tapes are almost purely beautiful — a characteristic not often associated with Dylan’s music.

Much of the beauty comes easily and obviously from Dylan’s accompanists in The Hawks, the musicians soon known as The Band, and the new mixes present them as the genius superheroes they were. There is the intuitive funkiness by second-string drummer Richard Manuel (filling in for the absent Levon Helm on most of the sessions) on “Silent Weekend,” “All You Have to Do Is Dream,” and elsewhere. Sometimes there no drums at all, like the buoyant “On a Rainy Afternoon” (still sounding gloriously like it came off a 78), and they are almost never the center of the attention. Everywhere, guitarist Robbie Robertson contributes complementary non-leads. There are ridiculous and braying horns by people who can’t really play horns (“Don’t Ya Tell Henry”), totally game silliness and high comedy (“I’m Your Teenage Prayer,” “See You Later, Allen Ginsberg”), and Manuel’s ethereal falsetto, deployed as tiny brushstrokes on three takes of “Tears of Rage” and as a heart-wrenching echo the perfect second run of “I Shall Be Released” that reveals all subsequent interpretations for the small tragedies that they are.

Bob Dylan always had a shtick: the Woody Guthrie knock-offs of his 1962 debut, the allegorical sing-alongs of the protest years, the biting comedy of “Like a Rolling Stone” and “Positively 4th Street,” the love songs of New Morning, his Christian records, the mystical poet of Desire, and on and on. Even the self-destructive WTF-ness of 1973’s contract-fulfilling self-titled album, Dylan, qualifies as a somewhat easily decoded stance. It would be ludicrous to call The Basement Tapes the “real” Dylan, or ascribe any purity of intent to them, but it really is another side of the Bobhead. For that matter, the mere size of the Tapes — some six-and-a-half hours of music — dwarfs any single period of his oft-changing musical persona, depending on how one wants to count the sprawling confusion of the 1980s.

Someone could (and perhaps even should) write a 33 1/3-style volume for each of the 139 tracks, but even that might not get any closer to the center of the Basement Tapes‘ secret. They are just songs, after all, not riddles to be solved, but places to visit and even live inside, like the perfect sleepiness of “Santa Fe” and “Too Much of Nothing (Take 2)” or the cryptical soul of “Edge of the Ocean” or the pastoral autoharp of “Auld Triangle” or the pulling piano of “Yea! Heavy and a Bottle of Bread.” The secret they possess — knowledge of the arcane and its proper deployment — is the kind of secret that keeps outsiders out and continues to welcome insiders in. It is a conspiracy of inside jokes to share with a group of musicians the listener will never meet — jokes that can never be embargoed because they’re still not meant for anybody else, whether they’re for sale or not.