David Upton posted:
"Mosby's analysis is highly detailed and below is only a sample summary of it...
....the spy told him where the enemy were on the night of the twenty-eighth when Meade's army was fifty miles away at Frederick. If this was the case, Lee had ample time to concentrate at Gettysburg. If he had this information, it is immaterial how he got it. Nobody can show that Lee did anything or left anything undone for want of information that cavalry could have given him.
......While the spy that is alleged to have appeared on the stage at night and to have changed the program of invasion is an invention for dramatic effect, a spy did appear in a commonplace way two days afterwards, when the army was on the march to Cashtown.... "

Here Mosby is incorrect. The Spy reporting on the 28th was not a fiction, but was "Henry Thomas Harrison"
He was first used by Longstreet in the Suffolk campaign in April, at which time he (Harrison) appeared with a letter of introduction from Secretary of War Seddon.
Anyway, by midnight, of the 28th, there was a courier pounding down the road north of Chambersburg bearing urgent orders to pull together the scattered elements of the Army of Northern Virginia/
Sears-"Gettysburg" pages 123-4.
By the way, where was Mosby at in late June, early July??