First Blood - S12-E9
Character mistake: Sam points out Elk Mountain, but there is no Elk Mountain in Rocky Mountain National Park.
The Song Remains the Same - S5-E13
Factual error: When Anna travels back in time, she lands on the hood of a Pontiac trans am. Castiel later comments Anna is in the year 1978, but the the Trans Am Anna falls has the front end of a 1979-1981 model.
Other mistake: Dean is tied to a chair when Sam rescues him. His hands are tied to the arms of the chair with rope. Sam comes over and just casually loosens the rope and it comes right off, then Dean just simply flings the rope off the other hand like they weren't even tied up, Yet before Sam got there, Dean was struggling to get loose.
Bloody Mary - S1-E5
Continuity mistake: When Jill's friend is saying how Jill died and mentions her eyes, she has her hands lowered in one shot but raised in the next. (00:16:11)
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)
Children Shouldn't Play with Dead Things - S2-E4
Revealing mistake: When Dean is talking to the girl about Angie, she's crying hysterically and using tissues yet there's no tears coming from her eyes.
Other mistake: When the guy goes to room 1444, the door slams behind him. He doesn't even try to open the door. He just shakes the door knob.
Revealing mistake: After Sam (Lucifer) beats the crap out of Dean's face, when he's sitting on the ground, you can tell he's got something stuffed in his mouth to make his cheeks and lip look swollen.
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.
Revealing mistake: The guy gets a pack of raw hamburger out of the fridge and starts shoveling it in his mouth. We can plainly see it's just red jello.
Simon Said - S2-E5
Factual error: The man gets hit hard enough by the bus to knock his shoe clear off, yet when we see his body about to be covered up, there's only a small amount of blood on his mouth. If you get hit by a bus hard enough to make your shoe fly off, then there should have been more damage.
Continuity mistake: In this episode, Dean says he was born in 1979. In the first two seasons, in the flashback to their mother dying, that's in 1983 which would make Dean 4 years old. He's definitely not 4 years old in the flashbacks.
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.