Pete has been playing ninth and thirteenth chords for years and an occasional diminished seventh. Some chords that Pete plays will never be found in traditional five-string banjo music. "Cocktail" is a style, I believe, and not a chord progression." Pete has a little knowlege of jazz harmony and is musically sophisticated. (He is an ex-tenor banjo player). I wouldn't be surprised if Pete could crank out a Ricky Martin or Barry Manilow tune with little difficulty. (Not that he would want to.)
Pete's banjo can play any music he wants it to and will not play by itself. I know because I've tried to play his banjo and I can't make it sound like Pete. He has the best Seeger-style basic strum of any banjo player in the world and that's because he adapted it from traditional sources and made it his own.
At the age of eighty-one, I give him credit for remembering the amount that still is in his head. If he forgets his banjo once in a while, it's forgiveable.