Thanks very much for the information. Johnston, in his "Battles and Leaders: Retreat From Gettysburg" essay claims he gave the message ordering Pemberton to move out of Edwards to Captain Yerger. The message, of course, was intercepted.
Somewhere, I ran across Yerger's account of this. He claims he rode all night, trying to find a path around the swollen fords and washed out bridges, and exhausted, settled down at a local inn. A member of Pemberton's staff was staying at the same inn, and offered to take the message to Pemberton's HQ in the morning. Yerger claims that he handed the message off and returned to his unit.
Have you run across that account before? Do you have any idea where I could find it again? I suspect, possibly, it was in "A Different Valor," but I can't seem to find that book right now.