Yes, we believe the flag is from the 46th Pennsylvania. The outstanding two book series "Advance the Colors" has many Pennsylvania flags listed as captured. The only problem is they name regiments that lost flags such as the (88th PA) but no info on where it was captured. We believe the 88th PA lost a flag at 2nd Manassas.
Many Union flags were captured at 2nd Manassas but not a whole lot on who lost the flags. I have several books on the battle.
It will take a long time to find these Union flags captured. But that is the fun of the "hunt".
Have a good day,