I don't know who Mary McFly is.
Doc doesn't know who Biff is, Doc is insistant on Marty not seeing HIS former self, they have different names, Marty isn't a scientist, Doc's shit on a Hoverboard and Marty actually dies in the alternate ending to BTTF 3, which would kill Doc but it doesn't.
( mike woz ere 7442200 & 7696970 getter, Thu 21 May 2009, 5:25, archived)

Well dur!
Marty McFly is obviously Doc Brown's dog Einstein from the future.
( Edd: The Unfunny Try-Hard Edgelord, Thu 21 May 2009, 8:30, archived)