Visible crew/equipment: In the scene before Dean makes the promise to Sam, as the camera pans along the side of the Impala, in the rear of the car, you can see the dolly track that the camera runs along.
Continuity mistake: At The End of this episode Dean suggests they go to the Grand Canyon because they have never been, later in the series they talk about John taking them when they were little.
Factual error: When the doctor says that the dead man has a high lymphocyte percentage indicating a viral infection after she looks down the microscope: 1) What they show in the microscope looks nothing like what is actually visible down a light microscope (especially the supposed lymphocytes) and 2) Even if she could see what they showed, it wouldn't actually indicate that the infection was viral.
Answer: Angel blades come from angels. It's their angelic magic that makes it special. Therefore, an archangel blade is made magical with the powers of an archangel. They couldn't have just created one or used one, as none of them are archangels.