Mr.Thompson,This used to be an active board.I still check it when time allows.I can't answer all your questions but,I might address a couple.First If he mustered in Aug.of 1861 then his term of service would have expired in Aug.of 1864 as the terms of service for regiments in this timeframe was for three years.Things changed as the war progressed. The 7th mustered in Apr.of 1861 for three months then mustered again for three years. Some of the higher regimental numbers latter in the war mustered for one year,so it depends.I am not familiar with the 28th.I had family in the 7th, 20th,36th,69th,113th,127th,141 Infty's.In general the originals could have veteranized,rejoined for the duration,or resign.The patriotism of 1861 wasn't the same as 1864.For a number of reasons.
Him mustering as a corp.might of been as simple as his ability to follow orders .His place in the community.In those days Regiments were formed from particular counties.At the company level it was in some instances from the same towns. Age.
I got to go.I hope this helps some.