Alan,
I seen you were confused about your ancestor Thomas Dobbs losing an arm and still continuing in the 23rd, if you take a good look at his records, you'll see they kept his rolls updated as "absent from wounds", so it looks like his military career stopped when he was wounded at Sharpsburg

Dobbs, Newton
mustered 8-31-61 at Camp McDonald, Ga. enlisted in Marietta
Admitted Chimborazo Hosp #5, 12-10-61 Remittens Febris returned to duty 12-17-61
Admitted Chimborazo #3, 5-14-62 Typhoid fever, transferred to Lynchburg, Va. 6-26-62
Admitted Gen Hosp #9, 10-14-62 transferred to Gen Hosp #21 Richmond
Admitted Gen Hosp #21 Richmond 10-15-62 Rheumatism, returned to duty 10-23-62,
22 yrs
Roll Jul/Aug 63 absent sent to hosp sick 8-24-63

Dobbs, Thomas
mustered 8-31-61 at Camp McDonald, Ga.
Admitted Chimborazo Hosp #1, 5-11-62 Diarrhea, transferred to Petersburg, Va. 6-26-62
Furloughed 60 days 10-12-62
Furloughed 30 days 7-3-63
Roll Jul/Aug 63 shows lost his right arm in action 9-17-63 and furloughed until 8-10-63 since at hosp
Roll Sep/Oct 63 present
Roll Nov/Dec 63 absent sick
Roll Jan/Feb 64 absent of Wounds
Roll Mar/Apr 64 absent of Wounds
Furloughed 130 days 2-18-63