Virginia,
I think you may be astonished, as I was, when I found the following image of the flag of the 18th Mississippi held at the Museum of Mississippi History (page down about 3/4 of the way):

http://mdah.state.ms.us/senseofplace/tag/flags/page/2/

What's remarkable is that this flag was captured by a New York regiment on May 3, 1863, the exact same day that William W. Beard was captured near Fredricksburg.