An interesting article on Gen. Brent is found in the 1909 Confederate Veteran, however, it does not help in answering your question.

Here are the two statements re his BGen.'s commission.

July 1864 Confederate Veteran found in Vol. 17, 1909, pp. 345-347, "Career of Gen. Joseph Lancaster Brent

"After reaching Louisiana , President Davis appointed him a colonel of artillery, in which position he won fame and a brigadier's wreath."

"In the latter part of 1864, in recognition of his splendid services, he was commissioned brigadier general of cavalry and assigned to the brigade consisting of the 2d, 5th, 7th, and 18th Louisiana Regiment."