The parole process at Vicksburg was quite similar to the process at Appomattox Courthouse almost two years later.
It took some time after the surrender on July 4th to print enough blank parole forms for the entire garrison. If you have a copy of this man's service file it should be evident that these forms were produced hastily on presses that appear to be quite worn.
Of course there also had to be some determination as to which Confederate divisions and brigades would be paroled first. Some commands received paroles as early as July 5th, while others had to wait several days before their turn came. It just so happened that Mobley's regiment was one of the earliest to be paroled.
Do you already have both service files?