Corrected entry: When they are at Belgrade, Poirot asks where Mrs. Hubbard is, and the conductor tells him that she is two compartments away. Poirot responds that she is still too close, which seems to imply that she was even closer the first night. But if you watch carefully as they get on the train at Istanbul, you can see that Poirot is nowhere near Mrs. Hubbard.
Corrected entry: The victim was stabbed twelve times, once by each of the culprits. But the Hungarian count and his wife held the knife together. There should only have been eleven wounds.