Re: 13th Alabama Regt.
What you found is a composite muster roll, not a roll call. Many of the men listed were dead, disabled, in prison or otherwise absent from duty and unable to answer a roll call. This is a register of all company members from original date of muster through Dec. 31, 1864. If you read carefully, you'll notice that it records whether or not a company member was present for each battle and skirmish in which the regiment was engaged.
Mathew Waldrop was captured during the fighting on South Mountain MD, Sept. 14, 1862, and exchanged a few weeks later. He was later captured during the first day's battle at Gettysburg PA, July 1, 1863, and imprisoned until released Oct. 31, 1864. He went home on furlough and was paroled at Talladega AL, May 22, 1865.