Bob Dylan had crucial second thoughts just as he was about to release “Blood on the Tracks,” the indelible 1975 album filled with songs of separation, heartache, sorrow, rage and regret. Now it’s getting a revealing close-up. “More Blood, More Tracks: The Bootleg Series Vol. 14,” due Friday, unveils all of the initial sessions: the solo, duo and small-group versions of songs that Dylan replaced, for half of the album, with more extroverted full-band recordings. There are an exhaustive deluxe six-CD version with every surviving take and a one-CD compilation of alternate versions of the album’s 10 songs plus one that was omitted, “Up to Me.”
