Our research has shown that the 75th OVI lost it's National during the assault on East Cemetery Hill on July 2nd.
From the History of Preble County, OH (by Audrey Gilbert) we learned that at 2nd Bull Run, every soldier in the Color Guard was shot and one of the guard dropped the Regimental to carry the National. When he was hit, Capt. (Later to be Colonel) Andrew L. Harris lead some men back to retrieve the National flag from where it's last bearer was shot. We believe that the Regimental was left on the battlefield and later captured by Longstreet's Corps.
In Sept. of '63 while the Regt. was on Folly Island in S.C. Maj. George Benson Fox writes home to his father asking him to please send them a flag. He wanted the National flag and he specifically says that "We want the Red, White and Blue" or National Colors. Not the blue flag or banner. Both are required to rig the Regt. properly but we only care about the National Colors".
He writes his father, again, on OCt. 24 for the flag. (His letters end in Oct).
The Regt. was presented by Preble Co. a flag to Col. A.L. Harris and the 75th O.V.V.I. This was given them after the Regt. was considered a Veteran Btn. while serving in Jacksonville, FL. This is the flag in the OHS: Ohio Save the Flags project.
I hope that the above info makes sense and answers some of your questions about the 75th's flag.
Please contact me re: the 145th Anniversary of Gettysburg and Ames' Brigade Reunion.
Maj. 75th OVI
A.A.G. Ames' Brigade