Originally Posted by Flyer23
Here's my question: If I were to check in online for my original LAX-DFW leg, but then not fly, could I also get the miles for that leg? Or is there a special switch that's only flipped when I actually get on the plane, which allows me to get miles for that leg?
The "switch" that is flipped is the scanning of your boarding pass at the gate. If your pass is not scanned, you don't get credit (for rather obvious reasons, as your post suggests). Scanning of one segment doesn't affect the second segment.