Nancy --
My wife's ancestor was a captain in the 17th Tennessee Regiment so I'm familiar with that command and other units in the same brigade.
The 23rd Tennessee Regiment reorganized a few weeks after the Battle of Shiloh, ten companies being consolidated into eight. The original Company "K" was given a different letter designation, so, from that time forward, this was an unusual case of a regiment that didn't have a Company "K".
The two regiments mentioned (17th/23rd Tennessee) acted together as a field unit, but companies did not merge. Each company continued to keep its own muster rolls. For that resaon you will find service records of members filed with the 23rd Tennessee, not with the 17th Tennessee.
During the second half of 1864 the Tennessee Brigade was released from service with Bushrod Johnson's Division and assigned to the defenses of the City of Richmond. I should have more than one inspection of the brigade, and there are numbers of communications in the Official Records about the brigade in 1864.
For some of the particulars about Company "K" and 17th/23rd Tennessee, see below:
http://www.tngenweb.org/civilwar/csainf/csa23b.html