Abraham Lincoln goes from being a brown-eyed boy to a blue-eyed man.
When Abraham is talking,the confederate beside him has his tie oddly to the right,in the next shot, it is backwards.
Teddy Roosevelt was born October 27, 1858 and would have only been 5 years old at the time of the story (based on the reference to the Gettysburg Address), not the teen boy shown in the film.
Stonewall Jackson was dead before the battle of Gettysburg.
Fort Pulaski came under Union control in 1862 a year before the film is set.
Pat Garret would have been eleven years old at the beginning of the civil war and only fifteen at its conclusion.
At various points as they enter the fort characters 'fire' weapons, mostly rifles, that are not cocked; the hammer does not fall yet the weapon discharges.
Toward the end of the movie, the South Portico of the White House is shown with the semi-circular balcony in place. That balcony was not added until the following century. President Truman had it installed during his term in office. It is still referred to as "The Truman Balcony".
When Garrett gets up from the ground after Pinn has left the fight (01:03) when you look behind him you can see traffic through the gate.
While clearing the town of zombies, a small tanker trailer with rubber tires is seen in the background in several scenes.
At one point, Lincoln steps out of a warehouse window on to a lower roof. The lower roof has asphalt shingles, which didn't exist until well into the 20th century.
Many of Abraham's men cut and slice however, in one scene a slice sounds like a slice, in others, a slice sounds like a jab.
When Abraham is about to light the barrels outside, his sickle is folded in, he hits two zombies, the second sound effect is a slash, not a whack.
Abraham Lincoln tells his men to shoot or slice the zombie's heads off or slit their throats, however Abraham himself slices one in half, and numerous men shoot their waists and that effect still kills them.
The writer throws in a racist, mustached Secret Service man by the name of John Wilkinson, as if to sow a seed that this may have been John Wilkes Booth. However, Booth was an American actor who had used J.B. Wilkes as a stage name, but never John Wilkinson. Considering all of the other veiled, but failed references in this movie, it is unlikely that this wasn't one, as well.