Thanks for those lines from Father Ryan's "Conquered Banner", a personal favorite when set to music.

Mr. Biggs should be quick to respond that his "theory" about the flag's identity as being that of the 12th Tennessee Cavalry. I'm sure he meant it as speculation, to be placed in the same category as your concepts about the flag being that of Rucker's Brigade. If we only knew more about the flag's origins -- who took it home after the war and how they acquired it. That doesn't seem possible now.