Friend of mine had a contrasting experience with the 'computer says no' approach of the airlines.
She was going to France last week with a car load of family and friends. They had booked the Eurotunnel train for 19:50. They found traffic on the M25 lighter than expected and arrived at the Channel Tunnel over an hour ahead of schedule. "Good evening madam, would you like to wait for your booked train, or take the next one?"
So, at no extra charge, they immediately drove to the departure ranks and left a full hour ahead.
That appears to be one of the ways in which Eurotunnel are separating themselves friom the airlines. Their customer is very happy and they also free up a space on a later train - in case they get more early arrivals, or a late booking.
It is so simple.