I am not an Xpert on the Vicksburg tragedy...But am curious as to weather the federals may have offered some type of devious incentive to actively serving Trans-Mississippi troops still under arms in Mississippi. Perhaps a few questions asked easy transport to their homes across the river along with the Paroled Trans-Mississippi Vicksburg prisoners. It would certainly be somewhat difficult to obtain the services of many of these soldiers later in the war.
MWT