It was quite common for a leading citizen to organize a company and once enrolled, offer the Company for state & subsequent Confederate service. Thereupon, it would be assigned a regiment and transported to a central location for actual formation.
As to the foot stone, I assume it is VA provided with the Southern Cross of Honor embossed. If so, the cemetery would have had to endorse the application and should have a copy on file, hopefully this would identify the person ordering. If not, the VA should have this, however, it could be a long time in getting them to reply.
Here is the info on the JW Ellis described.
John W. Ellis, age 18, Private, Capt. S. C. Pearson’s Company, Lieut. Col. J. S. Terral’s Battalion, Mississippi Volunteers,*enlisted April 20, 1862 in Clark County/Quitman by J. S. Terral for 3 years, promoted 5th Sergeant, n.d., captured at Vicksburg, Miss. July 4, 1863, paroled July 8, furloughed about July 20 for 30 days, reported to Parole Camp by October 18, 1863, exchanged December 20, 1863, captured at Blakely, Ala. April 9, 1865, transferred from Ship Island, Miss. to Vicksburg, Miss. May 1, 1865, , paroled at Meridian, Miss. May 10, 1865
* This company subsequently became Company E, 7th Battalion, Mississippi Infantry