As we aren't really sure WHERE the 3 machine + prototype are, it's absolutely possible that it's one of them,but equally possible that it's a fifth one we never heard about
Can you tell us in what years the machine was at her home, and in which state of the United States did his father live, and ideally, in which state did the machine end up (or at least a clue about the buyer?), unless he threw it in a landfill?