If Jazz has reached its full & final development?? It becomes interesting to know how harmony has been used in different jazz styles. Did Louis Armstrongs Hot 5's use only triads? What harmony in the Swing era? The Beboppers are better documented. How about Coltrane, Miles Davis, Charlie Mingus etc,etc. My interest & playing stops at Free Jazz, perhaps it doesn't use any harmony. But if we are going to perform styles from different eras we need to know our harmony.