Patzer

The letter Manfredi gives Holcroft, despite being 40 years ago, looks brand new.

When Noel returns to his apartment @ 18mins., the rain is falling on the umbrellas of the spectators but not on Holcroft.

When Tennyson/von Tiebolt shoots Oberst, the shot is heard before the pistol is fired.

Much of the film takes place in "Berlin", even though Berlin - and Germany - were still partitioned at the time, so it should really have been referred to as "West Berlin". Also, Holcroft and the Tennysons decide to travel from West Berlin to Geneva, Switzerland using ground transportation (driving and train travel), determining that flying would not be safe. However, prior to the reunification of Germany, ground travel between West Berlin and Geneva would have required traveling through East Germany, since Berlin was in East Germany. This was not easy for foreigners to do - requiring a lengthy approval process by the East German government, at a minimum.

Michael Caine's New York apartment has stairs in front because a London location was used. Manhattan apartment houses do not have a flight of stairs in front.

When Holcroft and a supposed bodyguard/helper are chasing the people who kidnapped Heiden Tennyson in Berlin the bodyguard/helper mentions to Holcroft's that his gun won't fire because the return spring is backwards in the gun he is holding. There is no way the bodyguard/helper could see inside the gun to know the spring was reversed. This also becomes a central theme at the end of the movie when Holcroft confronts Heiden.

Von Tiebolt and Kessler would not be permitted to bring guns into a high-security bank.

Holcroft failed to seek protection when his life was in danger.

In the latter part of the film, it is said that the Covenant has cost six lives, but the body count at that time is nine.

Because of the last minute change of lead actor from James Caan to Michael Caine, no adequate explanation is given as to why Noel Holcroft, the son of a German mother and an American stepfather who raised him since infancy, speaks with a British accent. If he had acquired the accent from spending his formative years in England, then he should not have had to have it explained to him by Helden that in Britain the word "boot" refers to a car's trunk.

When Holcroft called St. Regis hotel, he asked for Peter Baldwin in room 411, even though the phone message he received from Baldwin didn't mention the room number, only the hotel's phone number. Holcroft had never met or heard about Baldwin before so there's no way he could have known that.