That's been a mystery to me as well. Of course, Art's response may be as close as we can get to identifying the units in Villepigue's brigade at that time.
The mystery continues after the battle as Villepigue is detached by Pemberton to command a reserve force that is ultimately sent to Port Hudson. Reference is made to Villepigue's brigade, but the only unit of his brigade proper that accompanied him to Port Hudson was the 39th Mississippi. And, Isbell's battalion was also sent there, but to reunite with the balance of the 1st Alabama, and probably not as part of the reserve force or Villepigue's brigade.
As for Corinth, it is strange that Villepigue's report would mention only the 33rd and 39th Mississippi regiments. There is some evidence that Isbell's battalion of the 1st Alabama, and the 12th Louisiana participated in the Corinth battle.
Alabama Hist Qtrly vol 20
report of Corporal Partain 1st Alabama
indicates he was in the battalion that fought at Corinth since one of his letters was from Holly Springs on 10/20
Three Years in the Confederate Service Co K First Alabama Regiment by Daniel Smith
"....if Capt Isbell's men had no opportunity to win laurels in the battle, they won a glorious meed of praise as a portion of the rear guard...."
History of the First Regiment Alabama Volunteer Infantry by Edward Young McMorries
"...this battalion [Isbell's]...having participated in the battle of Corinth..."
Hugh Simmons 12th Louisiana website
Morehouse Stars Company F
James H. Stevens was Captain, .....Stevens commanded the company until he accidentally shot himself in the foot on the retreat from Corinth, Mississippi in October 1862
Jackson Greys 2nd Co M
When news of their declaration of exchange (agreed to at Aiken's Landing in Virginia on November 11, 1862) reached Mississippi, they were sent from Jackson to join the 12th Louisiana Infantry at Holly Springs, Mississippi .....
an old website
...brief account of their movements....
Oct 03-04 1862 Fought in the battle of Corinth.....
And, of course Art's indispensable Guide to Louisiana Confederate Military Units
....On October 3 and 4, the regiment fought in the Battle of Corinth.....
Prior to the Corinth battle, Van Dorn had apparently ordered Villepigue's brigade or part of it, to reinforce Breckinridge for his August 5th attack on Baton Rouge.
As with Bowen's brigade, they arrived too late to participate in the battle. References to them in the Baton Rouge campaign are as follows:
War Times in and around Clinton
In August, 1862, Gen. Lee [Union] and Col. Scott had an encounter at the Cross Roads, on the Baton Rouge Road, in sight of the old Monahan house. Gen. Lee was in command of two thousand Union soldiers, some of whom were convicts from the Baton Rouge Penitentiary. Col. Scott had about five hundred men at his command.
8/18 Gen Orders in the field -General Breckinridge cdg. Near Port Hudson,
I. In pursuance of orders from headquarters of department, Brigadier-General Ruggles will assume command of all the troops in this military district, except the Kentucky and Tennessee troops and the regiments from General Villepigue's command, now commanded by [Colonel] Scott
III. Colonel Scott will move his brigade independently of Colonel Trabue's brigade, but they will confer together and not separate far on the road, and will try to reach Camp Moore together early Friday morning.
8/29 Van Dorn at Vicksburg to Ruggles at Port Hudson Going to move north. Want all the men I can get. Think 2,500 or 2,800 sufficient at Port Hudson. Turn over command there to Beall and come to Jackson to take command. Send Twelfth Louisiana Regiment to Villepigue at once.
9/8 Spec Orders Dist of Miss, Jackson
I. Major General M. Lovell having reported for duty with this army is assigned to the command of a division composed of the brigade of Brigadier General J. B. Villepigue and other brigades to be organized.
10/1 Ruggles at Jackson to VD-The necessities of service have induced me to send Col Steedman's regt [1 Ala] Ala troops to relieve detachment at Port Hudson. Please send the men of his regiment now serving w/ Gen Villipigue.
As to other units with possible connection to Villepigue at Corinth:
The Zouave battalion has been mentioned [don't recall the source] in connection with Villepige at Corinth, but it is listed as a separate unit [as if unattached] in Lovell's casualty list for the battle of Corinth..
Sifakis shows the 1st Confederate battalion as being in the Corinth battle, but does not indicate a brigade assignment for that unit.
The 20th Mississippi was merely a fragment not captured at Fort Donelson.