The insult that sparks the hand-to-hand brawl between Dickinson and Adams is "Lawyer!" One of the first lines is "One useless man is called a disgrace, two become a law firm, and three or more become a Congress." Dickinson, Adams, and about 90% of the Congress were lawyers, so that seems a strange insult to use against somebody in the same profession.
John Adams and Martha Jefferson waltz during "He Plays the Violin". The waltz did not become popular until 1780, when it became the rage at the Hapsburg court in Vienna. It spread to other countries several years later.
John Adams and Benjamin Franklin make oblique illusions to Sandro Botticelli's painting of the Birth of Venus. At his death in 1510, Botticelli had lapsed into obscurity and was all but completely forgotten until a revival of interest in his works in the mid-19th century - Adams and Franklin would probably not have been familiar with him and his art.
Visible through the open door of the Assembly Room is the Supreme Court Room and on the wall is the coat of arms of Pennsylvania. This replaced King George's coat of arms which was torn down shortly after the first reading of the Declaration on Independence.
At the Congress, John Adams says "Benjamin Franklin smote the ground, and out sprang George Washington, fully grown and on his horse. Franklin then electrified them with his miraculous lightning rod and the three of them - Franklin, Washington, and the horse - conducted the entire Revolution all by themselves". Adams made that speech in April of 1790 at Franklin's funeral.
In the song "Lees of Old Virginia" Richard Henry Lee mentions General Lighthorse Harry Lee. In fact Henry Lee III, in 1776, was neither a General, nor had he yet become known as "Lighthorse Harry," a moniker that he would only earn after taking command of "Lee's Legion" in 1778.
When Adams and Samuel Chase talk about visiting the Continental Army, Adams asks Chase if he would support independence by saying, "Would you or wouldn't you?" When Adams says, "wouldn't you" his hand is clearly above the notepad on the desk (as evidenced by the shadow below his hand). In the next shot from behind Adams, his hand is resting on the notepad.
The circumstances of Caesar Rodney's ride are historically inaccurate. Rodney suffered from asthma and skin cancer, but he had not returned to Delaware because he was dying. As a brigadier general in the Delaware militia, he was in Sussex County monitoring Tory activity when he received word that the vote on independence was about to take place. Changing horses several times, he rode all night, eighty miles through a thunderstorm, to reach Philadelphia in time to cast his vote. He remained almost continuously in public service until his death in 1784.
When the Declaration is signed, John Dickinson leaves the Congress without signing the document. Though he was a non-signer, he did not resign. At the time the Declaration of Independence was passed, he was on the committee that drafted the Articles of Confederation (part of Richard Henry Lee's resolution).
While attempting to write the Declaration in his apartment, Thomas Jefferson throws the paper about and finally tosses his quill and picks up the violin. As John Adams and Benjamin Franklin enter the apartment, the quill has reappeared in the inkwell on the desk in front of Jefferson. But the change in lighting (from darkness to broad daylight) indicates that many hours have passed between the two moments.
Several times, Benjamin Franklin mocks John Adams for coming from Boston. Franklin himself was born and raised in Boston, leaving only in his late teens, but this part of his life was very unhappy, so it makes sense that he would distance himself from it.
After the song "Cool Considerate Men," McNair remarks that he could not borrow a dollar from any of those men. Although American dollars were not minted until 1792, Spanish reales were recognized as international currency, and called dollars by English colonists.
In the movie Martha came to Philadelphia to see Thomas Jefferson, as the two had not been together "for 6 months" - a common refrain by Tom. While Tom wrote the Declaration, Martha stayed in Virginia, recovering from a miscarriage - there is no record of such a "conjugal visitation." However, this was creative license on the part of Sherman Edwards and Peter Stone, who desired to show something of the Jeffersons' personal life without destroying the unity of setting.
A few characters want to retrieve the ailing Caesar Rodney from his home so Delaware will vote for independence. As Colonel McKean, explicitly states in one of the restored scenes, the delegation is tied without him, and would abstain. New York abstains on every vote, and no one worries about them. If unanimity is required, one abstention or two would have the same effect.
After the Declaration is approved Hancock asks the secretary if it is ready to be signed. The secretary replies that it is. This is not possible, as a deletion was made to the text only moments before, so no printed copy could yet exist.
Outside Independence Hall, the street is supposedly a dirt street, yet when the courier arrives on his horse, when Richard Henry Lee arrives on his horse, and when the "cool considerate men" drive away in their coaches, no dirt is kicked up by any of the horses' hooves. The "dirt" is artificial.
The beginning of the film takes place in early June, 1776 in Philadelphia. There are several references to the heat, and several delegates are clearly sweating. After a squabble breaks out during the debate, John Hancock orders McNair to remove a dog from the room because it smells bad. As McNair complies, Hancock shouts, "Christ! It's hot!" and Thomas Jefferson sits on a sill by an open window to read a book. In the next scene, the dog is out on the sidewalk. It barks twice, and you can see its breath.
After the song "Cool Considerate Men," as the delegates drive away in their carriages, one of the horses hooves slips on the ground as it makes its turn at the corner, revealing an artificial dirt road.