Continuity mistake: In the opening scene just before Victoria descends into the cave, she's wearing two headlights, the bigger one is on her right side and the smaller one is on her left side. In the next scene while she is talking to Josh, the position of those two headlights changed. (00:15:10)
Continuity mistake: When Conan first fights Remo, Conan places a blood stain on his forehead by pressing his sword to it. Remo then runs off, and Conan gives chase immediately, pausing only to get Tamara on his horse. The stain is still there when Conan mounts his horse. The next time we see them, Conan and Tamara is still chasing Remo, but now Conan's face is completely clean. It is highly unlikely he would pause in pursuit of one of his father's killers to wash his face. (00:47:55)
Factual error: Danny Greene has a bomb placed in Shondor Birns' car. As Birns is waiting to cross the sidewalk, the pedestrian walk-don't walk sign is a modern digital sign, that was not around in 1975.
Continuity mistake: Coulson has just entered the supermarket and is holding 2 donut packages in each hand. Watch his left thumb. In the close-up shot it is on the 'D'. In the next shot, it is below the letter on the red band on the plastic wrap. (00:00:55)
Factual error: Rochester Castle is seen standing alone and isolated from any other settlement. In actual fact it stands on the edge of the City of Rochester and very close to Rochester Cathedral, both of which certainly existed at this time.
Other mistake: When the captive begins her escape, she kicks the bed through the orange portal offscreen, but the portal only starts about a foot off the ground, so the bed would have hit the wall, rather than have gone through the portal.
Other mistake: At the beginning, the arrival board has the cities listed in alphabetical order, but "San Francisco" comes after "San Jose" when it should come before it.