Revealing mistake: As Dean digs into the dead guy's guts and discovers the claw the pale dead guy blinks.
Continuity mistake: When Sheriff Mills and Bobby are talking about transferring Rufus, her lapel goes from being under her seatbelt to over several times in subsequent shots.
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.