I've looked and I don't think this has been asked before. In Back to the Future 1, after Marty changes his parent's future, its obvious that he changes his own life and the life of his siblings drastically. He owns an awesome truck, has a date with Jennifer to go to the lake, etc.
So why doesn't he have any memories of these things? Shouldn't his memories be altered in the same way the photo of his siblings changes? Or an even better example: Doc's memories are different in that he now remembers Marty from the past and wears a bullet proof vest to the mall. And don't say that Doc always remembered Marty from the past and its a time loop because if that were true then Marty's family would always have been successful and his dad not a loser.