You're correct. The problem is this. I have a copy of the parole he signed 10 May 1865. Underneath his signature it reads 'Capt xxth Tenn Cav'. This is smudged and above it someone made the notation '11th', but the smudge could just as easily have said '10th'. Either way, this is the only record of his service I've been able to find other than index cards that refer to this parole. I don't have an enlistment record at all.
There is a mention in the OR of 'Sam Hardison's guerilla band' operating around Columbia TN in Nov 1864. I'm not sure where this date would fit into the location of the 10th TN Cav. You had mentioned that your ancestor had been in a partisan outfit before joining the 10th. Could there be a connection here?