Ken,
I would suspect that if they did have a "battleflag" that it was a homemade ANV style then and not one issued from a depot since the depot system was not yet up and running in late 1861.
I had an account of a flag being taken by the Fderals at Vicksburg and your note shows they actually had two flags then.
What's the source for the battleflag?
Greg Biggs