Apparently Mr. Spielberg made a whole bunch of real historical mistakes it his latest masterpiece Lincoln
Did he fuck up the flag? My guess is no, and that's my point.
He may have made a few choices or altered certain events for the story he was telling (I don't know, I've yet to see Lincoln) but my guess is he payed a lot of attention to certain details.
It's impossible to get everything right, but a flag isn't easy to fuck up unless you're just not giving a shit.