Continuity mistake: When Dean says he's going to talk to Amanda to get a grip on her mental state he has his head back on the seat and is looking straight ahead. When the shot changes he's now looking at Sam. (00:27:20)
Keep Calm and Carry On - S12-E1
Continuity mistake: Mary does not recognize adult Dean and claimed that her Dean is 4 years old. In Season 1 Episode 9: Home, she recognized adult Dean and Sam.
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.