In addition to the "Official Records," there is still material out there after all these years that has not been analyzed by military historians. Everyone wants to right about Bobby Lee, Stonewall, and J.E.B. Stuart but few want to travel all over the country to archives, libraries and make their eyes bleed pouring over stacks of documents.
For example, I can tell you that the greatest void we have in studying the history of the Army of Tennessee is during the Atlanta Campaign. If you look at the Compiled Service Records (CSR) of the regiments you will often see nothing during that time period unless they continued (or were able) to serve until the surrender. If a soldier deserted and was captured by the Federals that would generate a document and therefore we know what his disposition was. If an officer was wounded or died it would, the majority of the time, generate a document therefore we know what his disposition was. If an enlisted soldier was wounded or killed it may or may not have made it to a document that made it into the CSR.
There is a lot of material (emphasis, italic, exclamation point) that did not make it into the CSRs. Just one example, examine this link on "A Guide to the Samuel Hollingsworth Stout Papers, 1837 (1860-1865) 1902," at the Center for American History, The University of Texas at Austin, http://www.lib.utexas.edu/taro/utcah/00042/cah-00042.html
As far as I am aware, only two works have attempted to synthesis the material and they are "Confederate Hospitals on the Move: Samuel H. Stout and the Army of Tennessee" by Glenna R. Schroeder-Lein and "Two Confederate Hospitals and their Patients, Atlanta to Opelika" by Jack D. Welsh. Welsh's book includes a CD that has the Patient Rosters for Fairground Hospitals No. 1 & 2. Very few if any entries nor any others in the 1,500 lbs. of hospital records are not included in the CSRs.
Again, there is a lot of work to be done on the Army of Tennessee (AoT) and it can be done. The problem has been that the historiography of the Army of Tennessee was purposely "poo-pooed" (for the lack of a better description at the moment) by the likes of Jubal Early and many, many historians since then. Go to a bookstore this weekend and look at the Civil War books on the shelves. Look at how many are on Robert E. Lee, Stonewall Jackson, J.E.B. Stuart, the Army of Northern Virginia (ANV), or regiments in the ANV, or the Eastern Theater. Make note how many they are on the AoT, regiments in the AoT, or Western Theater. I believe you will be surprised. I can tell you, I am originally from Chattanooga, Tennessee and when I go back home and I go to the bookstore and look on the shelves, most of the time the books on the shelves are Eastern Theater and it is not because the Western Theater stuff is outselling them.
I hope this helps.
Respectfully,
Gerald D. Hodge, Jr.
War Between the States Historian
M.A. Military History - Civil War Concentration
Historian: 39th Georgia Volunteer Infantry Regiment
http://39thgavolinfrgt.homestead.com/39thHomepage.html