During the first scene, Leonard's hands are bound with black cable ties; after the camera shows the enemy entering the room and throwing the picture at him, the cable ties are now white.
Near the end when Harry shoots the Russian bad guy, he fires a Beretta 8000L Cougar (beveled slide). In the next shot he is holding a Glock pistol (squared-off slide).
When Harry tells Leonard that he is joining the agency it is 2015, or 10 years after the opening sequence, which is revealed to be 2005. He then apparently spends at least 2 years in the agency applying and being rejected for field work. Yet, the end of the movie takes place still in 2015 as shown on the grave at the end. Where did those 2 or more years go?
CIA officers do not carry sidearms, unlike FBI agents.
The Smith and Wesson Airweight has an internal hammer, yet when Victoria points the gun, you can hear the sound of a hammer being cocked. (This happens again when Harry uses it.) It has a 5-shot capacity, but after Harry puts one round in the pistol and rotates the cylinder (which would not make that typical movie clicking sound), he pulls the trigger five times.
At the beginning of the film, when Bruce Willis calls his son, after his mother is shot, he says,"go upstairs, in my dresser, on the left side"; but the gun is on the right side and is in the night table.
During the opening training montage, Harry is shown running along the waterfront. Prague is in a land-locked country with the nearest port 500km away. Explanation - Harry is focused on his goal and continues his training even while traveling in Mobile, AL.
In the beginning of the movie a short scene shows an airport with a control tower and a ramp. This is Berlin Tegel Airport. The Taxis carry German license plates with the first letter a B for Berlin.
Near the end, they show the Arlington National Cemetery as "Arlington National Cemetery Washington D. C." Arlington National Cemetery is in Arlington County, Virginia, across the Potomac River from Washington, D.C.