Ken,

What is your source for this capture? The 50th Illinois' only combat action at Donelson was the afternoon of February 15th, 1862 when as part of Cook's Brigade along with Lauman's Brigade of Charles Smith's Division, they assaulted the Confederate works on their right flank which was held only by 9 companies of the 30th Tennessee Infantry (the tenth was manning heavy guns at the Water battery).

Of course the flag could have been found within the fort after the surrender as many were.

Greg Biggs