I think the 12th Ga art batt'n must have been issued another flag after they lost it at Fort Steadman. In the catalogy of the Museum of Confederacy they have the 12th Batt'n Ga Heavy Art as captured at Saylor's Creek by the 1st Conn Cav. There was a * next to the picture meaning, based on modern research.
I see they have another * next to the 18th Ga Batt'n Inf. Says believed to have been captured during the Appomattox campaign, April 1865. Does not state Union regiment that captured it. Otherwise there are no other flags in their collection of the 12th or 18th ga battn's

Shawn