Neither George or Lorraine recognized Marty?
In the new timeline that he created by being the one that Lorraines's father hit, there was too much going on for them NOT to remember him.
He is the one who got them together, (something that women don't tend to forget), and the effort he put forth with George (including the traumatizing visit from Darth Vader from Vulcan, are 2 events that they wouldn't tend to forget.