Webster's work contains the following:
Polk, N. R. Co. E, 38th Mississippi, date of death: 8 Jun 1863. Under Remarks:
"UDC Record page 35, (Carried in the UDC Record with date of death as
7 Jun 1863)
The previously published listing of "Confederat Soldiers Buried at Vicksburg, February 15, 1862-July 4.1863", compiled by Carolyn Reeves Ericson and Frances Terry Ingmire, 1981, contained the following in the preface:"This list has been typed from a dim copy of a list from the Mississippi State Archives. When a letter or number was in doubt, the character used has been underlined to indicate this uncertaninty."
On page 46 we find:
Polk, W. H., Col. M. 33 Miss, died June 7, 1863 ['W', and 'M' are underlined.]
Recorded from UDC Book #35.
Obviously, these are the same persons. Old records are difficult to read for a number of reason and transcriptional errors abound.
I do not know how Gary came up with these corrections.
A tombstone may be placed in Confederate rest, but would not represent where he is buried, if at all in the cemetery.
I suggest you contact the local Vicksburg UDC Chapter or SCV Camp for