You probably will never know any more than what you do, but you might get lucky some day. I met a fella whose g grandfather's record showed him as discharged disabled after Shiloh. The family had always thought he must have been wounded in the battle. However, I found a diary that told what had happened. While marching on the retreat from Shiloh, the guy stumbled in a hole and torn his knee very badly. He hadn't been wounded at all!