Originally Posted by Mr. Tickets

People will dispute this, but I had a friend who was recently booked on two separate tickets that were supposed to be in the air at the same time. One reservation had his SkyMiles number in and one did not (on purpose, so that they would not be able to track the duplicates). Delta DID catch it and called him to make a decision on which he would be using. They have made some major strides in tracking these things.