Its worse than you think, Bryan. The asterick gives no hint as to the number or nature of the boodles and boodles of documents that were not selected for the O.R.
Here are the original books (hardcover ledgers, really) for the U.S. Army of the Frontier, 1862-1863, that I found during a frantic three-day blitz in the National Archives a few years ago.
ARMY HEADQUARTERS
General Orders
Letters Received
Letters Sent
FIRST DIVISION (Blunt)
General Orders
Letters Received
Letters Sent
FIRST BRIGADE (Salomon), FIRST DIVISION
General Orders
Letters Sent
Special Orders
SECOND BRIGADE (Weer), FIRST DIVISION
Daily Journal
Letters Sent
SECOND DIVISION (Totten/Huston)
Daily Journal
General Orders
Letters Sent
Notice that some books seem to be "missing." For example, in the First Division there is no Daily Journal for the First Brigade and there are no Letters Received for the Second Brigade. Notice, too, that there is nothing at all from Herron's Third Division. Are the books gone? I don't know. What I do know is that I needed more than three days to carry out a thorough search. (Needless to say, I did not have time to rummage through regimental records.)
Trans-Mississippi Confederate records in the National Archives are slim (because so much ended up in the Alexander Papers at Columbia and the Herron Papers at the NYHS, I suppose) but Union records contain a surprising amount of useful information about Confederate activities.
For what its worth, my guess is that there is a huge amount of Trans-Mississippi material out there, but it has been largely ignored for the past 140 years and is scattered and misfiled and poorly inventoried. We are the first generation to really dig into the stuff. And as we all know, being the first ain't easy.
How I do run on. My apologies.