Just a pity that the Confederates didn't think a little more about posterity and make a record of what flags were captured.
Regarding Wheat's Battalion casualties at 1st Manassas. The official report of casualties was based on surgeon W. S. Love's report. Written soon after the battle, Love didn't get it right. From records these are the casualties for Wheat's Battalion at the battle of July 21 1861:
Killed in action - 5
Wounded - at least 50 (five mortally wounded)
Captured - 2
This works out to about 15% casualties. However, while the casualy rate seems low (one member of the Battalion said that the low casualty rate was because many Yankees hadn't set the sites properly on their rifles), very few escaped unscathed, but only some 50 were wounded so badly that they required hospitalisation. Wounds were so common that one soldier cut himself with a knife so that he wouldn't stand out from other members of the Battalion.
I am pretty sure that none of Burnside's Brigade (1st RI, 2nd RI, 71 NY, 2 NH, Rhode Island Battery) lost their colours in the morning battle (where Wheat's Battalion fought as a unit). Did the 11th NY lose their colours - I'm not sure. I am not even sure whether any of Wheat's men engaged the 11th NY. However, Wheat's men did have plenty of chances to find colours. This was because, as the Battalion fragmented after the morning engagement, the men of the Battalion ended up distributed across the battlefield. While spread out many took the opportunity to gather souvenirs during and after the battle. Maybe that is members of the Battalion had the chance to pick up the colours.