Then there is the "I'm Not There" part. This is the title of a Dylan song. The lyric from the chorus is,
But I'm not there, I'm gone.
As the title of the film, it has multiple meanings and stands alone, even with out the 'suppositions' part, as all but a disclaimer that Bob Dylan will not be found in this endeavor.
Just the name of the film, then, has not one but two statements admitting to the impossibility of the project.
It's as if the title disarms criticism with a preemptive strike. Right away we know that Haynes' intention is to explore the various ideas about Bob Dylan that have currency in popular culture and yet he is not willing to commit to being able to do more than speculate about them.
This is true of anything - a film, a book, a painting - 'about' anything really. But specifically, there is no definitive in this film because there is not a definitive Bob Dylan. Even if we break him down into the clichés or archetypes, there are just too many contradictory Dylans. Like young, sexy blue suede shoe Elvis and old white jumpsuit Elvis, both are somehow the real Elvis that negates the other version of him.