The film’s title, “A Complete Unknown,” serves as a guide for how it approaches its subject material. Mangold’s script works to uphold the mythology of Dylan as an unknowable artist — who, from the beginning, was reluctant to be defined by others and by himself. 

While shooting his new film “Birdman,” director Alejandro Gonzáles Iñárritu handed his cast and crew a photo of Philippe Petit making the high-wire walk between the Twin Towers of New York’s World...