There were no company or regimental records after November 1864 which survived to be recorded in the National Archives Compiled Service Records.

Hence, we have no idea of casualties after that date through the end of the war.

You best best would be to contact the regiments "expert" who developed the web site I posted earlier.

61st Tennessee Infantry csa863@hotmail.com (Chris Propes)
http://www.fokh.org/61st%20Home.htm

I subscribe to Footnote.com where I can access the Confederate Compiled Service Records which should be the exact records which you hold for William.

Good hunting,

George Martin