Unfortunately, Brent's memoirs ended with his service in 1862, and don't cover his subsequent service in LA.
He was paroled in 1865 as a Brigadier, which I consider the best evidence of the promotion. It was a Kirby Smith assignment to duty, like DeBray and others had. In addition, Brent commanded colonels in his brigade and needed that rank in order to command them. My book has a 10-15-64 assignment date.
There are a lot of Brent papers scattered among various archives. I wish I had the chance to more thoroughly go through them.