Without trying to be unkind, you may want to check the dates that Shiloh and Vicksburg were fought.
Then go to the Gerdes site and see what it has to say about his group.
If he died in 1867, in my opinion, it would be possible for him to have been wounded at one of these
battles and that death came years after due to the nature of his wounds.
Good luck in your search.
Linda