The American Civil War Research Database has him promoted to full Colonel Aug. 31, 1863. This is not supported in the records. I assume their information is found in the Official Records. I tried a search there, however, there are too many Thomas’ in the records for an easy search.

…

Henry P. Thomas

Enlisted on 7/19/1861 as a Major.
On 7/19/1861 he was commissioned into Field & Staff GA 16th Infantry
He was Killed on 11/29/1863 at Fort Saunders, Knoxville, TN
Promotions:
* Lt Col 2/15/1862
* Colonel 8/31/1863

Sources used by Historical Data Systems, Inc.:
- Roster of Confederate Soldiers of Georgia 1861-1865
- Official Records of the War of Rebellion