The first time the cigarette case is opened, to signify the owner's Nazi sympathies, the engraved swastika is reversed, the open-ended bars pointing downward. At the end of the film when the same cigarette case is opened, the engraved swastika has been corrected. Obviously 2 separate cases were used - one correct, one not.
When the explosive-laden ship out at sea is about to be bombed from the air, the stock footage of the bombers shows them clearly over land.
At the end, Garrick mentions that the cigarette case with the swastika inside saved Sally's life when she was shot by the Nazi Orlock. However, the cigarette case does not appear to be damaged.
When the passengers of the ship are being checked by Canadian Customs upon arrival in Halifax, Major Fothergill walks right past the agent, following Mrs. Towcester, without showing his passport or being questioned.