If you had no photo reference, after 25 years, you’d probably have just a hazy recollection.
So, many years later, they still might remember that interesting kid who got them together on their first date.
Bear in mind that George and Lorraine only knew Marty/Calvin for six days when they were 17, and they did not even see him every one of those six days.
But I would ask anyone to think back on their own high school days and ask themselves how well they remember a kid who might have been at their school for even a semester.