The Alabama in the Civil War Message Board

My great grandfather William Marshall Funderburg

I would like to get some help on some questions I have about my great grandfather's Confederate service record.
William Marshall Funderburg was from St. Clair County, Alabama, From the official records, he entered service somewhere arounf December 1863. There is a pay receipt for the period of December 1863 until sometime in 1864, for the 12th Alabama Infantry. He then, appears on muster rolls at the Talladega Camp of Instruction in Company B.
Other documents, such as hospital records, pay receipts, and two muster rolls show him in Company D of the 12th Alabama Infantry. There is also a record showing of his capture the day after the battle of Monacacy. His death at Elmira prison camp is also listed as well as his burial site at the cemetary in Elmira.
My questions are.....was he conscripted and sent to the 12th? There were no companies of that regiment from anywhere in St. Clair County. Also, a book on the history of the 12th shows him in Company I, then later Company D. His muster rolls show he enlisted for the war in April 14th 1864. Would that have been consistent with a conscript, to enlist for duration of the war? Lastly, where would I find information about Confederates captured after the battle of Monacacy. I would like to know the circumstances, and location. In reading Lee's Lieutenants, it states that the number captured were few, but were left behind by Early's arm. Can any of you guys help me out on these questions?