When Watson walks into the front parlor for a conversation with Sherlock, he closes a book he is reading. The shot moves to Watson, but just a moment later Sherlock once again closes the same book before he speaks.
The coin Al-Asmari shows Joan was minted by Alexander the Great. It could not have come from the sunken Spanish galleon as claimed.
Clarence Drummond describes a flag with "SCUBA snorkels", but snorkels are not needed for SCUBA (Self-Contained Underwater Breathing Apparatus). They are only used while wearing SCUBA so that the valuable compressed air is not wasted when the diver is near the surface, but they are not bespoke SCUBA equipment.