The Confederate flag that is referred to as a Confederate Battle Flag is actually the Confederate Naval Flag, only used by the Confederate Navy. A true Confederate Battle flag was square.
The main characters are carrying weapons on what they describe as being the actual site of Pickett's charge on July 3, 1863. The National Park service does not permit re-enactors to carry weapons on any national park grounds. Re-enactments are actually held on private property.
At one point a note on the screen states that Pickett's Charge is being made on July 2nd, 1863; however, historically it occurred on the Third of July..
The confederate lieutenant says that they have been transferred to another corps, that of General George E Pickett. It was Pickett's division in Gen. James Longstreet's Corps. George Pickett never commanded more than a division.
When Gen. Lee walks through the camp, he has three stars on his collar, indicating the rank of a colonel. A general's rank has three stars enclosed in a wreath.
Colonel Devine tells his troops if they win at Gettysburg they can "march through the Shenandoah Valley to the steps of the Capitol". The Shenandoah Valley lies in Virginia, well to the south and west of Gettysburg and would take the troops away from Washington DC. The actual path from Gettysburg to Washington DC is due south, through Maryland.
The battle happened in early July of 1863 although in the scenery all of the trees have already lost their leaves. Even in Pennsylvania it would be the most verdant time of year.
At one point Col. Devine says that the "yankees" are gathering on the high ground north of town. The federal positions were south of town.