The flag did originate from the Middleton family and Arthur Manigault's middle name was Middleton, so that part is solid with me.
His brigade had some Alabama regiments in it besides the two SC regiments so it could be one of those and Manigault, as brigade commander, retained one of the flags when the new AOT flags were issued in early 1864. I just wish there was a better paper trail for this flag - but it is indeed authentic. Howie Madaus knew about it from some years ago.
Greg Biggs