If I understood it correctly, Vance got out of active service due to a detached retina...which was exactly what the dead guy had, so I'm not sure of exactly what it means but it leads to a few possibilities:
- Vance isn't who he says he is (even to his family)
- Vance's friend pretended to be him to get him out of active service
- I missed something and am way off the mark
personally I'd go with option C :)