Update, on another June, 1862 Regimental Return for

John Palmer
Enlisted on 9/1/1861 as a Private.
On 9/1/1861 he mustered into "I" Co. AL 21st Infantry

"Died, was left at Memphis & heard of his dealth June 26"
Date of alteration on June, 1862 Regimental Return

This would indicate, the actual date of death was unknown.

The Regimental Return for Thomas makes the same note, i.e., "Date of alteration - June 17"

Again, this would indicate, the actual date of death is not certain. And could be only the date they became aware of his passing.