Thankfully that phase of the Mills Brothers' formidable legacy has been documented more than would be expected. They were so far ahead of the curve that they still set the standard of excellence nearly eighty years after the fact. The tragic and early passing of oldest brother John Junior (seen in the clip playing guitar) in 1936 was an immeasurable loss. Genius of the highest order.
And of course these were all numbers that were filmed for the feature "The Big Broadcast" but were either cut from the film or didn't make the final cut. It would be interesting to edit them back into the film.
