Factual error: When Hitler signs the diary, he writes in a modern way of writing. But in the late 30s there was a different style of writing called "Suetterlin". The letters looked quite different from nowadays. (01:10:25)
Factual error: When Hitler signs the Grail Diary, in the screen and VHS release he signs Adolph, not Adolf. This mistake was corrected in the DVD release. (01:07:35)
Continuity mistake: When Indy gives his father water from the grail to drink, the grail glows from inside, and the gold inside it is bright and even. But when Indy pours water over the wound, the grail is dark inside and there are dark patches in the gold. Obviously, they had to take the light that made the grail glow out so it wouldn't be seen when Indy pours the water over his father.
Revealing mistake: When Kazim dies, his shirt is all bloody, but there are no holes in it. The bloodstains looks painted on. (01:26:30)
Continuity mistake: The 109s that are animated are shaped like the original German fuel injected ones. The shots where it's a real plane show the modified one with a RR Merlin engine that gives it a weird square nose.
Factual error: There are no catacombs in Venice! There are also no natural petroleum sources - but that seems secondary to the fact that the entire city is just below sea level - there are no sewers, no subways - nothing underground.
Continuity mistake: As Sallah pulls Dr. Jones senior off the tread of the tank, Indy lets go of his whip and turns towards the German colonel and they continue fighting face-to-face. You can see that Indy punches the colonel so that he loses his balance and stumbles backwards. A split second later, the colonel is standing behind Jones with his arm around Indy's neck. They did not have nearly enough time to so radically change positions. (01:32:15)
Other mistake: When Indy and Kazim are fighting on the the boat as it is being chewed up by the giant propeller, the propeller is more than half way out of the water; if the ship was in dry-dock the smaller boats wouldn't be able to go up to the larger ship, on the other hand if it had run aground it would not be running its engines.
Continuity mistake: When Indiana pushes the Nazi colonel out of an open window, if you look carefully, the colonel fell a few metres out of the zeppelin before landing on a pile of suitcases, but when the colonel looks up, the zeppelin is several hundred metres above him, in too short a time to ascend that much.
Factual error: Indiana Jones checks his dad's grail diary to find the picture of the stained glass window in the church in Venice. With the book open to that page, the picture is on the left-side page, and under Indy's thumb on the right-side page is a snippet of an article about marriage statistics. The article mentions statistics up to and including the year 1943. Problem is, the movie takes place in 1938. (00:27:00)