Something else that leads me to believe that the "mystery" dismounted Texas cavalry regiment was a mistake in the order of battle (which I think was caused by the 12th Texas Cav.'s original orders being changed) rather than an actual additional cavalry regiment is that on pg. 102 of A Texas Cavalry Officer's Civil War: The Diary and Letters of James C. Bates by Richard Lowe and James Campbell Bates it says regarding the massing of Van Dorn's Army of the West units for transportation across the Mississippi River that "In addition to Sterlin Price's Missouri militia and other infantry units, sixteen regiments, one battalion and three companies of cavalry milled around the river landings, ready for departure to Tennessee and Mississippi."

Now this might be sort of an odd way to confirm it but if you'll bear with me I'll explain my reasoning. Sixteen cavalry regiments is exactly how many would have ended up in Corinth had the 15th, 16th and 17th Texas Cav. Regts. not been detained in Arkansas in response to Samuel Curtis's threatening movements. The 14th Texas Cav. Regt. was the only one of the four to make the trip all the way as it was the first to have made it to Little Rock in the first place. But those other three didn't ultimately get sent across so if you count the thirteen Texas cavalry regiments from Van Dorn's army that made it to Corinth plus the three (15th, 16th and 17th) which didn't but were originally intended to, you get sixteen cavalry regiments. Meaning if this mystery cavalry regiment supposedly in Dabney Maury's brigade was really present at Corinth it would make seventeen rather than sixteen, meaning there was no "____ Texas Cavalry Regiment (dismounted)" that was present but simply unidentified in Maury's brigade, it is almost certainly a mistake in the ORs' order of battle probably caused by the 12th Texas Cavalry Regt. being originally earmarked for Corinth and going to Memphis but being sent back. Lowe and Bates must have used the ORs' order of battle, discovered that the "___ Texas Cav. Regt. (dismounted)" didn't actually represent a unit that was truly there but not have discovered the truth about the 15th, 16th and 17th Cav. Regts. Make sense?