Factual error: Cary Grant arrives at his Tokyo hotel two days early, and no rooms are available. He goes to his embassy, which, according to the sign on the gate is the "British Embassy". In reality, the sign would say, "Embassy of the United Kingdom of Great Britain and Northern Ireland".
Other mistake: When the three roommates take a taxi, Christine and Steve quibble over the fare, eventually handing their portion to Sir William. However, he never does pay the cabbie, rather he goes off to confer with his driver, Jimmie.