I am doing genealogical research on my forebears. It is amazing some of the documents that emerge. Many, at the time, no doubt trivial. One piece was my grandfather's handwritten notes of when he was up country in Tibet and when he was back in Calcutta. Fascinating stuff and a regular cycle. Seems about 9 months after each detachment ended my grandmother had a child.
What I am trying to say is that your ancestors might hold such trivia as a valedictory letter as very important.