The archived records are important because they are all we have. We were not there so any tid bit is a great find. They give you an idea of what was going on but not the whole truth. Today U.S. military historians, there are service men whos job this is, are a small number, usually one per command. They only record the highlights of the command for the year. Details are not normally covered but in some cases where required. I don't recall and don't know if any existed in the Civil War.
The problem with military record keeping is the high turn over rate of units. Even in peace time, the same administrative or supervisory job which would produce or save these records is turned over to someone else on a yearly to two year basis. This was a problem I had in the military, is the historical record keeping was so bad.
You have to take what you find with a big grain of salt.