When Rollin recreates the diagram made by the three Nazi guys, he adds the "T" to the word "cemetery", which was not shown on the projection screen. He also omits the black rectangle that was to the left of the word "CUNO" on the projection.
Hitler's first name is misspelled as "Adolph" on the "Mein Kampf" prop book used. The correct spelling is "Adolf".
The astrological timetable the Nazis use - Venus in Pisces, Sun in Gemini - is impossible. As one of the two planets closer to the Sun than the Earth is, Venus is always within two signs of the Sun; if the Sun is in Gemini, Venus must be in Aries, Taurus, Gemini, Cancer, or Leo.
Rollin says that the picture postcard has never been mailed. He can't know that. It could have been sealed in an envelope then mailed. His correct statement should have been "That's a picture postcard but there is no postmark so it wasn't sent through the mail as it is" or something similar.
There is no explanation of where the fourth watch came from, or why Rollin had it in the first place, but pretended not to have it.
After Briggs has listened to the tape of the 'mission' briefing, he destroys the tape reel by throwing it into a furnace as he passes in his car. If you look carefully as the camera pans to the furnace you will notice the reel in the bottom of the frame as it misses its target and bounces back off the floor.
During the phone dialogue between Briggs and Rollin, it was mistakenly implied that the city of Rio de Janeiro is located in Argentina. However, Rio de Janeiro is actually situated in Brazil.