A Very Supernatural Christmas - S3-E8
Revealing mistake: When the boys are tied up and the pagan gods are preparing for the ritual, the second time they cut into Dean's arm the knife is pressed along his arm and the blood is removed showing no cut at all.
A Very Supernatural Christmas - S3-E8
Continuity mistake: In 'A Very Supernatural Christmas' (S3E08), when the Gods are beginning to sacrifice Sam and Dean, they slice Sam's right forearm. However, at The End of the episode, Sam has his left forearm bandaged, not his right.
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.