You might check with the National Archives to see if there is a pension file on him. If so, it might shed some light on your ancestor. While most militia veterans who served in Missouri were not eligible for federal pensions, the Provisional Enrolled Missouri Militia was an exception (as was the Missouri State Militia). If your guy lived long enough after the war to collect a pension, and/or if his wife filed for a widow's pension, there should be a fair amount of information in his file. In fact, the largest Civil War pension file I have ever run across, by far, involved a veteran of the PEMM.