One of the three whip marks on Milner's back is missing when he escapes his captors and backs away down the ship's corridor.
When Thompson's two henchman are trying to outflank Cardigan, the gray-haired henchman, who is wearing light coloured trousers, runs from the left of the shot and passes behind a rock. However, the man who emerges from behind the rock, and is immediately shot by Cardigan, has dark hair and is wearing dark trousers.
When Milner bumps into Cardigan on the stairs, one of the bullets on Cardigan's hunting vest has slipped almost all the way through the holder. In the next shot, all of the bullets are in place and evenly aligned.
During the island shootout, Dan (Mitchum) keeps holding his gun up when not firing. While this is standard gun safety practice, Mitchum seems to forget that enemy combatants are supposed to be in front of him, so it would be best for his character to keep the gun aimed at them, even when not firing.
The weight and balance of the Bonanza would preclude two people in the back seat and one in the front.