A s the passing of time undoes established norms, the contemporary music world keeps updating the meaning of that collection of styles often bundled up as “classic jazz”. In the 1940s, the modernist bebop movement was jazz’s uncompromising cutting edge, and the music’s early 20th-century roots in street music, plantations, saloons and red-light districts became its classic trad forms. The artwork for Twio Vol 2. Photograph: Melissa Cohen/Blue Note Thirty years later, bebop’s breakneck melodies and jarring chords became “classic jazz” themselves, overtaken by the free-improv avant garde of Ornette Coleman and John Coltrane, the jazz/rock fusions of Miles Davis, Weather Report and Frank Zappa, and new jazz-influenced folk and contemporary classical forms from all over the world. In those creatively dizzying years, jazzers still wanting to play song-tunes and old-school swing sometimes found themselves mocked by progressives as sad nostalgics.…