Factual error: When David talks to Linus about the consequences of calling off his engagement with Elizabeth he says that their father would take to the bottle and smoke six coronas. Throughout the movie the old Larrabee smokes one churchill after another, but not a single corona, which is significantly shorter than a churchill.
Factual error: At the beginning, when Sabrina describes the Larrabee family, she says that David is listed as a $600 deduction on Linus' income tax return. Two problems: 1) Shortly after Sabrina goes to Paris, Linus is shown sending David a memo to remind him that he is a junior partner in the family company, and is eligible for retirement - based on his one year with the company. 2) Both David and Linus still live with their parents. If David could be claimed as a dependent, I should think it would be by his parents.