That reminds me of the story about a balladeer who attracted national attention for his vast knowledge of Appalchian folk songs. Several song collectors came to hear him do a live concert hoping to uncover some rare song that he knew.
He started the concert out with a rendition of "After the Ball was Over" not realizing that the song was a popular hit in 1896.
I've done several concerts with Country Music Hall-of Famer Doc Watson. I had to shake my head when I heard him play "Nights in White Satin," a song I didn't know he played.