This topic comes up from time to time in Western Swing threads, including the current Western Swing arpeggios thread. I would like to hear from you knowledgeable Jazz historians. Western Swing bands played a wide range of tunes, including copying the arrangements of current popular tunes. The question is: what was the standard I chord played in the Swing era, non-Blues (mid 30s to mid 40s?)? Triad? Sixth chord? Not major seventh during that era?