Given that his company was aware of his capture, July 10, 1864, I'm inclined to believe that he indeed did catch up with his regiment and participated
in the Battle of Monocacy.

Communication being what it was in those days, it seems doubtful that his comrades would have been aware of his capture had he not been with them.

Only a guess on my part.

"William M. Funderburg, Private, Company D, 12th Alabama Infantry, recorded on his companies Sept. & Oct., 1864 muster roll as absent, taken prisoner July 10, charged with arm & accoutrements $73.63"

I suspect he lost his equipment prior to his hospitalization at Howard's Grove.