Recently, speculation has turned to just what kind of 70-year-old John Lennon would have been if he hadn't died. In the case of Bob Dylan, we don't have to speculate: He's the kind of septuagenarian who will play the White House and not so much as fist bump the president and the kind of mensch who doesn't forget friends like Dave Stewart (he co-wrote a song on the Eurythmics co-leader's new album). He's also an ex-hoarder who has gradually learned the power of unburdening himself of a lifetime of musty treasures. This week Columbia released The Witmark Demos: 1962-1964, the ninth volume of the Bootleg Series, and arguably the most revelatory of all of Dylan's castaways. Once upon a time, he really was the voice of a generation. And somehow, he still is.