A couple of errors should be cleared up here.

First, in April 1863, the 1st Confederate Regiment was stationed at Fort Gaines near Mobile. Many of the original companies in this regiment began their service at Pensacola, but the city had been evacuated in May 1862. In April 1863 five companies of this regiment at Mobile were ordered to the Army of Tennessee at Tullahoma. The rest followed a year later.

Second, the reference on roll to Jonesboro GA is dated Aug. 31, 1864, not Aug. 31, 1863. That was a mistake in another post.

There are several ways for a soldier's name to be removed from roll. These would be death (any cause), discharge (any reason), desertion, transfer or promotion. Death, discharge or desertion during the period Sept. 1 - Dec. 31, 1863 are far more likely. However, in case of desertion, a soldier's name might sometimes be kept on roll longer, just in case he returned to duty, so the first two are most likely.