User blog comment:Thetwindler/Dropped/Discarded Ideas throughout the seasons/@comment-98.115.189.149-20200205132736

On the wiki there is something about Dean's blood type possibly being O, mentioned when Sam got "your blood type" to purge demon Dean. There is some question about whether that means Dean's type IS O, or just that O is the universal donor type so wouldn't hurt him. However, John's dog tags list AB, so if Dean's type is O, he can't be John's. I was rewatching Season 5's The Real Ghostbusters. At one point, Sam and Dean are talking, and Chuck is heard talking to the convention in the backround, stalling to keep the crowd in the room. I thought I heard Chuck say, "John isn't their father." So if he's not their father  that's kind of a big piece of info to drop. Also really makes me wonder, well then who is?