The history of postwar American abstract painting remains a work in progress. We are barely beginning to understand its sheer multiplicity in terms of the artists’ races and cultures and the works’ physical character. New information arrives in regular and humbling batches. The latest is Joe Overstreet’s stunning exhibition “Innovation of Flight, Paintings 1967-1972” at Eric Firestone. With 20 rarely seen works, it covers a brief period when Mr. Overstreet’s disavowal of painting’s usual standards and practices was unfolding rapidly in several directions, alongside efforts by Sam Gilliam, Harmony Hammond, Alan Shields and Howardena Pindell, among others.