Early in the film some packages are delivered to the office in
which Redford works. The security guard counts 5 of them, and says "Roger, fiver." The NATO phonetic alphabet uses "niner" for 9 in order to differentiate the sound from "fife" for 5. No retired military man, as the guard is supposed to be, should say "fiver."
Joubert is portrayed as a highly efficient, methodical assassin. However, in the scene in which he kills Atwood, he places the gun in Atwood's hand to make it appear that he committed suicide. Any competent killer would realize that the police would have found no gunshot residue on Atwood's hand, thereby immediately debunking the suicide cover-up.
Janice tells Turner, "Your calligraphy's getting beautiful." This would not be a realistic response from an actual Chinese person, in light of the fact that Turner (Redford) writes the "tien" completely wrong. A real Chinese friend (romantic or otherwise) would have taken the pen from his hand and shown him how to write it correctly.
When the Condor is in Kathy's apartment, they watch a news
report about the shooting in the alley. The reporter has a channel 7 microphone and identifies himself as being with Eyewitness News, the name of WABC-TV's news broadcast for decades. When the report is over, we see the logo for channel 9 instead of channel 7.
When Turner is given the report from Langley saying they found nothing to be concerned about in the book he read and reported on. Turner folds it and puts it in his right rear pocket. When he tries to remember the section chiefs name the morning after at Kathy's apartment, the morning the mailman comes, he retrieves it out of his left rear jeans pocket.
The housing development in which Sam lives is the Peter Cooper Village apartment complex in the Gramercy section of Manhattan, which was built as middle-class housing in 1947 but was converted to luxury market rate in the 2000s. When Turner rings the doorbell, an electronic buzzing sound is heard, but the apartments in the complex have actual doorbells that make bell sounds.
When the Condor is getting soaked by rain on his way to lunch, everyone immediately around him has umbrellas. There is a man in the distance to the right of the police officer, obviously oblivious to the rain and walks as if he is beyond the reach of the rain machines.
As Condor opens the desk drawer of the dead receptionist to grab the gun, the .45 automatic moves too quickly when barely tapped by his fingers to be an actual gun made of normal wood and metal, revealing it as a balsa-wood prop.
When Turner (Condor) buys a pretzel from the street vendor, between handing him the money and receiving his change, he bites into it, revealing that it is a small, hard pretzel, and not the sort of pretzel sold by a vendor.