I believe the men you list were captured, wounded who died in Yankee hospitals and subsequenly buried in
idetified graves.

Sgt. Peter Williamson, Co D, 5th Rgt. Wounded 7/3/1863 Gettysburg, PA (Severely wounded in right leg, amputated)

Wm. Stevens, Co E, 5th Rgt. * POW 7/2/1863 Gettysburg, PA
* Wounded 7/2/1863 Gettysburg, PA (Severely wounded in right leg, amputated)

J. C. Graham, He died wounds POW on 8/29/1863 at Gettysburg, PA
(Died at Camp Letterman Hospital)
* POW 7/2/1863 Gettysburg, PA
* Wounded 7/2/1863 Gettysburg, PA (Severe wound in left elbow)
Buried: Gettysburg, PA Gravesite: row 6; #17