John Adams and the fourth of July myth

Just finished "John Adams" by David McCullough, which I've enjoyed as much as any political biography I've ever read. I knew nothing about him until I saw the HBO mini-series. If anything, that series undersells him.

John Adams and Thomas Jefferson were known as the voice and pen respectively of the American Declaration Of Independence. Their lives, while completely different, were intertwined. They both served as President. They both lived far longer than any of their contemporaries and died, hundreds of miles apart, on the same day, the fourth of July, 1826, which was the nation's 50th birthday.

Although the declaration is dated July 4th it was actually passed by Congress two days earlier and celebrations didn't take place until July 8th. At the time Adams said that July 2nd would be the date that would go down in history. According to McCullough's book Jefferson actually spent July 4th shopping for ladies gloves. However in later life both Adams and Jefferson bought into the national tradition so completely that they would argue vehemently that it all happened on the fourth. So much for primary sources.