Factual error: When Bill and Ted grab Beethoven, we are shown the piano he was playing which is a Steinweg (Steinweg later changed his name to Steinway when he immigrated to the United States). Steinweg made their first piano in 1835, and the model shown was built in Braunschweig so must have been made after 1858, but Beethoven died in 1827, years before a Steinweg piano existed. Also the onscreen graphic says it's 1810. (00:47:50)
Factual error: When Bill, Ted, Billy the Kid and Socrates end up in the future, Billy and Socrates are told to stay in the phone booth. Socrates nods and remains in the phone booth. In Greece, nodding means no.
Factual error: During Bill and Ted's first time traveling in history, Rufus states they are in Austria in the year 1805. 1805 was the year Napoleon achieved his greatest victory over Tsar Alexander I and Mikhail Kutuzov at the Battle of Austerlitz (present day Czech Republic). Napoleon didn't invade Austria until 1809.
Suggested correction: Austerlitz was part of the Austrian Empire. But that battle was after the Battle of Ulm. After Ulm surrendered, Napoleon advanced to Vienna and took the city. The Austrian War did occur in 1809, but that was Austria attacking to free neighboring countries under Napoleon's rule.