He was only talking about published materials, not the reams of unpublished meterials that are still present, such as all the materials and records that are in the National Archives captured at Richmond and other places, which have not been evaluated, such as hospital records, for their information. Not counting the large number of private diaries and journals which are in private collections, or where privately printed in small numbers and are little known. Just in the last few years were the supplements to the O.R.'s published. Materials left out of the original O.R.'s when they were published.
It is the "Nuts and Bolts" researchers, the private researcher looking for a single purpose, who digs these "Nuggets of Gold" out of the rubble of those records. It is not normally the writters, or the readers of comtempoary General History that discover these things, for the scope of their subject, or their interest, is too vast to relate the inner workings that was the American Civil War. It is like the Linebacker who tackles the entire football team looking for the one quarterback that has the ball.
And as one writter I have spoken too about why books are not written about the situational climate and politics of the war especially on the southern side, his reply was "Battles sells books, politics don't". Yet, the Civil War was a political war. It is only on sites like this that a differing viewpoint, other than the conventional wisdom and thinking, is even explored.
My point in all this, is that while there has been much that has been written, and even that several subjects have been written and rewritten about multiple time to the point of boredom, like Gettysburg, there is much which hasn't been written about also. Because it does not sell well. The main purpose of writting a book is to sell it. And like you have said these authors are mearly looking to their own interest of searching for "New" subject materials, that would be of interest to enough buyers, to write about from the people who are researching the tinest special interest details.
It would be interesting to hear what these writers have to say, if they were of a mind to contribute rather than sit on the sideline. But they have a position, and their self interest, to protect. No University level history professor, or nationally noted writter, is going to post openly on this, or any other board, and risk their reputations should their unconventional thinkings and statements become known to the politically correct outside world. And if their viewpoint is conventional wisdom, then we have all heard it before, haven't we?
It is only we who have nothing to lose who can take openly and frankly of our opinions.