For decades now, Bob Dylan has been shadowed by The Bootleg Series.

The live cuts and collections of unreleased tracks have done deep dives into prolific periods of his illustrious past, pulling the curtain back for fresh perspectives on revered albums and reassessments of less highly regarded works.

Now at long last, we've arrived at Blood on the Tracks. The 14th volume in the series takes on the heartrending 1975 album that is the quintessential masterwork of the mature Dylan — who will bring his Never Ending Tour to the Met Philadelphia on Dec. 3.

More Blood, More Tracks (Columbia / Legacy *** ½) digs into the archetypal breakup album that gave the world "Tangled Up in Blue," written while Dylan's marriage to Sara Lownds was falling apart. A decade after he had reshaped popular culture as a young man with a mind of fire, it captures Dylan still at the height of his powers, weary with the ache that comes with the passage of time.

The cover of Bob Dylan’s “More Blood, More Tracks.”
Columbia / Legacy
The cover of Bob Dylan’s “More Blood, More Tracks.”

This volume doesn't arrive with a treasure trove of previously unheard songs, like such recent Bootleg editions as 2013's Another Self Portrait, 2014's The Basement Tapes Raw, or last year's Trouble No More, which opened up the vaults on Dylan's late '70s-early '80s Christian period.

Instead, More Blood delivers alternative versions of the original's 10 songs, with 87 tracks in a six-disc deluxe box, all recorded over six days in sessions first held in New York, and then with different musicians in Minnesota when Dylan was dissatisfied with the initial results.

Bob Dylan.
Ken Regan
Bob Dylan.

Only three songs on the set are not heard on the original. The strummy "Up to Me" proudly reaches for the artistic brass ring rather that settling for the mundane. A tender take on the traditional "Spanish Is a Lover's Tongue" is the lone nonoriginal. And the bitter and bereft "Call Letter Blues," has the same musical arrangement as Blood's 12-bar blues "Meet Me in the Morning" with entirely different, harsher lyrics.

More Blood shines light on Dylan's creative and decision-making process. There are multiple versions of beloved songs like the pained "You're a Big Girl Now" and agitated "Idiot Wind," often with alternative rhymes and slightly different arrangements.

What's remarkable about the set is how varied and excellent all the tracks are, almost without exception. Emptying-the-vaults projects with multiple takes are often maddening, with only slight variations rewarding to obsessives.

Bob Dylan.
Barry Feinstein
Bob Dylan.

But if Dylan wanted to do another Blood take, it was because he had a worthwhile idea to try. And in this instance anyway, he was fully committed to each performance. Another reason to hear More Blood: On the original, tracks were speeded up slightly to give songs added sting. Shorn of that effect, Dylan sounds deeply relaxed and self-confident as a vocalist, with many versions arguably superior to the originals.

That said, six discs of alternative takes is a bit much. More Blood is arranged chronologically in the order the tracks were recorded, so two or three versions of "Buckets of Rain" or "Simple Twist of Fate" are often strung together. It can get repetitive and annoying. Happily, there's also a single-volume edition that consists of single alternative takes of the original album, plus "Up to Me." If you're not really deep into Dylan, get that one.