The Benders - S1-E15
Factual error: Officer Kathleen looks for Sam's data in her database. The record ID is DF-23094. She then follows the link to Dean's record. Its record ID is also DF-23094. A database cannot have two records with the same ID.
Factual error: At the beginning of the episode it is stated that we are in the month of April - yet in the orchard there are ladders, fallen apples and baskets filled with fresh fruit everywhere, as if it were harvest time. The god is declared to grant fertility and not climate change, so the harvest decoration seems definitely out of season.
Factual error: At the beginning of this episode, it says "one week later", then it shows Dean and Sam go to the victim's apartment. The blood is still bright red. After a week it would be darker.
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.