Audio problem: When Dean puts the cassette in the car stereo he reads 'Metallica' off it, yet AC/DC plays. [In the original version Metallica was played, but AC/DC was used in newer versions due to copyright issues.]
Audio problem: The pilot asks Amanda how she is at the start. When Amanda replies the audio doesn't match her mouth. (00:02:10)
Provenance - S1-E19
Audio problem: When Sarah goes to touch Evelyn's shoulder, you hear Sam's voice telling her to stop, except his mouth isn't moving at the time the phrase is being uttered. (00:23:50)
What Is and What Should Never Be - S2-E20
Audio problem: Dean is in the cemetery talking to his father's grave, trying to figure out what's happening to him. In a continuous shot, right after Dean says "like it doesn't want me to be happy", you hear him say, "of course I know what you'd say" but his mouth doesn't move at all. (00:23:00)
Audio problem: When Dean and Castiel are speaking to the police officer, Dean and Cas say "nothing" and "demons" at the same time. The second time this happens, Cas' voice says demons but his mouth is not moving. (00:11:55)
Mannequin 3: The Reckoning - S6-E14
Audio problem: In 6.14 "Mannequins 3: The Reckoning", when Dean goes up to talk to Ben, Ben is playing a video game. Dean says something along the lines of "There's no way plants could kill zombies", therefore pointing out that Ben is playing Plants vs. Zombies, but the sounds coming from Ben's gaming system are not from Plants vs. Zombies.
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.