Also, consider the large number of casualties suffered by the 34th Mississippi Regiment during the Battle of Perryville. Warren W. Jackson must have been among those who died of wounds.
One of the 'givens' about regimental research concerns records like this that have been misidentified. This isn't the result of an error, but some records have been misfiled because clerks at the War Department made mistakes. Also bear in mind that the National Archives has another data source for records that were never filed.