I get the feeling that he would not have sung himself unless he felt he was good enough...
In about 1971, I heard him live in Winfield.. with Merle. Some group in the audience kept teasingly shouting, "Sing, Merle!"
   Doc finally leaned up to the mic and said, "No, he's not going to... to tell you the truth, I don't believe the boy CAN sing!"

Everyone shut up, kinda startled. It was hard to tell how serious he was, but Merle did not sing.