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.
Suggested correction: Mary was a ghost in "Home" and knew that 22 years had passed and her sons would be older now. When the Darkness resurrected her, it was without the memories of her time as a ghost. Mary said so explicitly.