Particularly obscure? 
I was just wondering about the description of "I'm Not There" as being "particularly obscure." Before being released on the I'm Not There soundtrack, it appeared on both The Genuine Basement Tapes and Tree With Roots bootlegs, which are in widespread circulation among Dylan fans, and it doesn't seem to me any more obscure then the dozens of other unreleased tracks on those bootlegs. In fact, it got a lot of ink in Greil Marcus' Invisible Republic/Old, Weird America and I can't remember off the top of my head if Clinton Heylin talks about it a lot, but I always thought it was quite famous in its own right as one of the "great, unreleased" Basement tracks. Well, it's possible that is just my perception, but I think if in doubt we should lean towards neutral language and simply refer to it as "a previously unreleased track" or something like that. Or directly quote Marcus or Heylin or someone for a description of the song.