Throughout the film, Vallo's tan appears and disappears, varying between those shots filmed on location in the Mediterranean and ones later filmed in the studio in Britain.
Vallo wears red trousers when he, Ojo, and the Professor are abandoned in the small boat. When they're adrift, he wears gray trousers (minute 61/63).
While fleeing from the soldiers to establish themselves as rebels, after the hidden trampoline jump from one building to another, the light source in the last window obviously changes.
When Humble Bellows is lowered over the side to listen to Captain Vallo speaking to Consuelo about his releasing her and her father, Humble is hanging upside down. When we next see Humble up on deck, he is soaking wet. Why drop him in the water, when deck side is only a body length and a hand up away?
When the King's men capture the pirate ship in the harbor and throw the drunk pirates overboard, the first pirate that is picked up has a yellow head covering, white shirt, tan trousers, and boots; when they show that pirate being thrown overboard in close-up, he has a gray head covering, torn dirty white shirt and dirty yellow trousers and boots; when they show that pirate hitting the water, he has no boots.
When Humble Bellows on Baron Grud's ship looks through the telescope at Vallo and Ojo rowing towards the ship, the shot looking through the telescope shows them rowing away instead of towards.
At the beginning of the film the ship taken by pirates with the ruse of stricken ship scurvy. Although referred to as a British ship, the flag that brings (which incidentally seems an invention) has a section of the arms of Castile and rather Spanish colors: gold and red.
When Captain Vallo pulls a man overboard (at the beginning of the film), the man is wearing sailors' clothes, but when we see him fall into the water, he's wearing a uniform. That shot was intercut from the climactic battle scene at the end, when the same shot of the same soldier falling into the ocean is repeated. Secondly, the man being pulled into the water is standing on the deck of the ship, but when we see him fall, he falls down from a mast.
When the rowboat collides with the wall, it is evident that it is made of painted canvas stretched over a frame as it wrinkles and then stretches back out.
Several times aboard ship the ship's wheel is spun but the rope tiller lines, which control the rudder, do not move. This is clearly seen as the wheel spins but the rope remains still.
In the final fight (circa 1:39:30), Ojo falls onto some enemies (and gets a barely seen bump on his back). Less than three minutes later, the same shot (about one second long) is repeated.
When the King's men capture the pirate ship in the harbor and throw the drunk pirates overboard, footage of the same pirate is used twice, but out of sequence. First, a pirate with a torn dirty white shirt, gray head wrap, and dirty yellow trousers is shown being dropped over the side, then a few seconds later the same pirate is shown being picked up before being tossed over.
At Cobra, the view of the signalman through the spyglass is at the wrong angle. The signalman should be facing the ship head-on, but the view of him through the spyglass is from below him and to the right.
In the background of both shots showing the old crew tied up in the net is a luxury ocean liner.
When Bertha shouts at the party, "It's the Crimson Pirate!" her voice and her mouth movements clearly don't match.
When the green-clad dance troupe enters the formal gathering, Vallo's mouth is not in sync as whispers to Ojo, "Bertha, that dame we held for ransom."
At 32 minutes when the Crimson Pirate and Ojo are escaping to the ship in a rowing boat, Humble looks at them through a spy glass and sees their faces as they move away. From his vantage point on the ship, they would be coming towards him and he would see the backs of their heads.
Humble Bellows makes some grammatical errors in his use of the "thee" dialect, using the word in contexts like "thee art" or "thee canst" when it should be "thou art" or "thou canst" (He's probably not well educated).