Problem --

Jeremiah W Stallings of Co "D", 13th Alabama Regiment was wounded at Sharpsburg MD, Sept 17, 1862, and lost a leg due to amputation above the knee. He never returned to duty. That rules out Lieutenant Marks, who was wounded at Gettysburg on July 1, 1863. Ken can verify, but the 13th Alabama did not lose a flag that day.

More likely that Stallings remembered the wound taken by then 1st Lieut Algernon S Reaves at Sharpsburg.