When your debut album drops in between the assassinations of Martin Luther King Jr. and Robert Kennedy and mankind's first steps on the moon — and your second gig is at a little outdoor get-together called Woodstock — "generational" is a difficult tag to avoid. Few still-active groups wear it as well as David Crosby, Stephen Stills and Graham Nash, who last month provided The Tonight Show with its best bit since Johnny Carson's departure: the trio crowding around Jimmy Fallon (as Neil Young) for a harmony volley of Iggy Azalea's rap smash "Fancy." (Fallon/Young: "Trash the hotel." Crosby, Stills and Nash: "Let's get drunk on the minibar.") The irony fades quickly upon consideration of CSNY 1974 (Rhino), a ruby-anniversary, triple-LP and DVD remembrance of the band's fated "Doom Tour" that arrived the next day, amid a barrage of press anecdotes from the road to ruin — sex, drugs and rock 'n' roll, mostly in that order — and how, at its tattered conclusion, the closest voices in counterculture folk hated each other's guts. It's all the more reason to pull a Fallon, add your voice to the chorus of "Teach Your Children" and be thankful that the times, they're still a-changin'. Tickets $79.85-$120.85.