We have discussed on this board before the flag taken at Fussell's Mill/second Deep Bottom in August 16, 1864. The captors claim it as the flag of the 10th Alabama.
In checking a number of sources, but in particular the historian at Richmond NPS, there were no Alabama troops at all involved in the line when the Uhion attack broke it, which is when the flags were taken (6 claimed in all that day).
The Confederate troops holding the line were Girardey's Georgia Brigade (formerly Wright's). He was killed and his brigade seems to have lost three of the flags taken that day - one by the 39th Illinois and at least 2 by the 85th Pennsylvania (their report claims three).
Based on what GA units were part of Girardey's Brigade, the only unit with a "10" in their designation was the 10th Georgia Battalion. Thus, most likely, this was the flag taken by the 39th Illinois that day.
This is not the first time that unmarked ANV battle flags were mis-identified by their captors. I know of several of these instances offhand.
Hope this was of some help.