I think we have to remember this is his son's book and contains portions of selected letters. It's not a complete work listing all of Gen. Lee's letters.
A more complete collection is Clifford Dowdey and Louis H. Manarin, eds., The Wartime Papers of Robert E. Lee. Lee wrote to and about Longstreet a lot, but those letters for whatever reason weren't included by his son.
Regards,
Cash |