Continuity mistake: When Sadusky has Ben handcuffed across the desk from him, there is nothing on the desk directly between Sadusky and Ben except Sadusky's coffee mug, a gray thing that is about mid-way between Ben and Sadusky, and a white spiral notebook to the right of the coffee mug. Then Ben says, "Ian still ended up with the Declaration of Independence," and as the shot switches from Ben to Sadusky saying, "Because of you," we see the glasses Ben found at Independence Hall appear on the desk in front of Sadusky between the gray thing and himself. Then as Sadusky says, "Someone's got to go to prison, Ben," and Ben says, "Yeah," two short stacks of papers appear on the desk in front of Sadusky and the glasses changes position as well.
Continuity mistake: This concerns National Treasure 1 and 2. In the first film, when Ben's grandfather tells Ben the story about the clue given to Thomas Gates, he says he was the grandfather's grandfather's, grandfather - Ben's Great, great, great, great grandfather. In the film, in 1832, he appears very young, maybe early 20s. But in the second film Thomas Gates, Ben's Great, great grandfather, appears to be 40-50 in 1865. A young man in 1832 can't have a middle aged grandson in 1865.
Character mistake: When Ben, Riley, and Abigail are in Independence Hall in Philadelphia and roll out the Declaration of Independence to inspect with Ben Franklin's special "ocular device" that Ben had just found, Ben pauses to take in the moment. When asked what was the matter, Ben says "It's just that...the last time this was here (in Independence Hall)...It was being signed." However, according to archives.gov, "In 1876 the Declaration traveled to Philadelphia, where it was on exhibit for the Centennial National Exposition from May to October. Philadelphia's Mayor William S. Stokley was entrusted by President Ulysses S. Grant with temporary custody of the Declaration. The Public Ledger for May 8, 1876, noted that it was in Independence Hall "framed and glazed for protection, and... Deposited in a fireproof safe especially designed for both preservation and convenient display." Sorry Ben.
Other mistake: The signature on the copy of the Silence Dogood letter is different than the one on the original. They should be the same if it was truly a scan.
Continuity mistake: When Riley is cutting into the pipe holding the cable for the National Archives, the hole he cuts changes shape after the shot showing him examining the wires. (00:31:35)
Continuity mistake: When Ben is trying to pay cash for the 'replica' of the Declaration of Independence in the Gift Shop, he lays his wallet down on the counter and starts counting out bills and change right next to his wallet on the counter. A few scenes later, when the FBI is reviewing surveillance tapes, one of the monitors shows Ben reaching in his pocket, pulling out his wallet and grabbing the money that is out on the counter. This happens when the over voice says, "Charge. Benjamin Gates."
Other mistake: When Ben enters the Gala dressed in overalls and tool belt, he enters a door across the street from where Riley is parked. There is a security guard outside that door who waves Ben on into the building. As Ben exits that same door, there is no security guard, which seems hard to believe with such a big event.
Deliberate mistake: In the two scenes when Ben and Riley are in the documents room, it is in full light. The rotunda is actually dimly lit as a way of protecting the documents from light damage.
Continuity mistake: In the catacombs under Trinity Church, the lift Ben and Abigail are standing on falls. When it jerks to a stop, Abigail falls and Ben catches her. The lift is stationary at an angle. However, in the next shot, the lift is swinging forwards, allowing Ben to throw Abigail to safety. (01:40:00)
Visible crew/equipment: Three times you can see lens flare as the camera is pointing towards the sun: the airborne-shot of the Jefferson Memorial (in this one you can even see a part of the airplane or something else in the lower left corner), the Philadelphia skyline as they drive into Philadelphia, and the view from the "target location" of the shadow of the cross (near the brick containing the glasses) towards the steeple with the bell.
Other mistake: In the scene where Ben, Riley, and Abigail arrive at Patrick's house, the location title at the bottom of the screen says, "Philadelphia, PA." Then, as the Declaration of Independence is being examined, Patrick says that he donated the Silence Dogood letters to "The Franklin Institute in Philadelphia." Finally, as the scene ends, Ben, Riley, and Abigail are in Patrick's car, driving through the night towards Philadelphia. (00:55:55 - 01:04:15)
Continuity mistake: When Riley is in the subway to get the video footage, he starts to record the preservation room that shows the declaration on the desk, but how can It be there if Riley hasn't used the laser to get it moved there yet?
Continuity mistake: When Ben and Ian get into an argument over stealing the Declaration of Independence, Ian says "all you're going to be is a hinderance." Shaw then points a flashlight and a gun at Ben. When the camera angle is on Ben, there is no flashlight beam visible on him. Then Ian says, "I'll shoot your friend", Shaw points the flashlight and gun at Riley, the light beam visible on his face. Ben lights a flare. Shaw points the flashlight and gun back on Ben, and again, no flashlight beam is visible on him.
Continuity mistake: After everyone gets off the elevator down under the church, Ben has the declaration of independence then Riley has it without Ben giving it to him.
Revealing mistake: When Ben is pulling the dumbwaiter to the secret room with the rope, there is a shot showing the bottom of it. In this shot there is a somewhat visible black wire that is pulling the dumbwaiter, rather than the thick orange rope that is pulling it. (01:46:15)
Revealing mistake: When the stairs built on the walls of the dumbwaiter shaft start to collapse, Riley makes a jump onto a stable one. In the first shot of him jumping you can see a thick stunt wire attached to the back of his shirt. (01:43:35)
Character mistake: After cracking the clue of Silent Dogood letters, while leaving the shopping mall, Riley asks Ben and Abigail, "Who was the first to propose daylight saving time?". They reply "Benjamin Franklin". But, it was George Vernon Hudson in 1895.
Plot hole: The tunnel at the base of the stairs under the church wasn't connected to the stairs and seems to only have been reachable with the elevator system.
Factual error: The poem on the pipe stem reads Fifty Five in Iron Pen, and Nicolas Cage states "a document that fifty five men signed." The Declaration of Independence was signed by fifty six men.
Deliberate mistake: When Riley uses the video camera laser to disable the Declaration of Independence sensor, that could never happen since cameras are not permitted in the documents room.
Answer: He doesn't simply assume "Beneath Parkington Lane" means beneath the church: Parkington Lane is the name etched on the tomb hiding the entrance to the tunnels. When he saw it, he naturally deduced what he had to do.
Sereenie