Just came across this "google book." States the 9th New Hampshire took the 23rd Tennessee's flag. One or both, not sure. This would have been in June 15th-18th, 1864. About 600 Confederates were captured and five flags. The 23rd and 63rd Tenn regiments were in the third Brigade. Sounds like they were hit hard, maybe the other flags belonged to the third brigade.

http://books.google.com/books?id=2IkvAAAAYAAJ&pg=PA168&dq=Union+colors+captured+during+the+Petersburg+Campaign&lr=#v=onepage&q=&f=false

Google book website,

Hope that helps Greg,

Have a great weekend!

Shawn