Gary, Thomas Jefferson and Isaac E. Howell orginally enlisted in CO H, 20th. Miss. Infantry. TJH was captured at Fort Donelson and IEH was not. While the 20th. was imprisoned Isaac enlisted in the 39th. Miss. Infantry in May/1862 and was eventually dropped from the rolls of the 20th Infantry. Thomas J. was transferred to the 39th. Inf. on Oct 20, 1862 after being exchanged with W. C. Puckett.

Sgt. Isaac E. Howell was serving as a member of CO G, 6th. Regt. Miss. Cavalry at the end of the war.
http://mississippiscv.org/MS_Units/6th_MS_CAV.htm

Military service and pension records may be procured at this site -
http://history-sites.com/research/index.html