I wonder does the book mention the POW/MIA issues of wars prior to VN?
I understand the focus of VN as it's more recent history and deals with men who's names are known here, but VN isn't the first time the U.S. knowingly left men behind.
As early as WWI Soviet Bolshevik forces captured and held allied and American prisoners. The Soviets wanted recognition of their government.
In WWII a large number of allied soldiers “disappeared” at the end of the war. These were men still in or returned to German POW camps in territories that fell under Russian control. It happened partly as a result over, IIRC, the Yalta agreement dealing with POW exchange and the returning of Russian political prisoners to Russia. A number of those Russian POWs being men who fought with the Germans against Russia. Last the Russians wanted money.
To a lesser degree it’s claimed POWs were lost during the Korean War.
I’d read a book some years ago that had researched the earlier POW/MIA issues, unfortunately I can’t remember the name. The following websites have some of what I remember from the book.