If it was a joke, the joke was on me. I did not doctor that in any way, I assure you.

And yes, you SDC by choosing the "Change" link after clicking the Check In button. It's rather hard to find and not obvious that what you are doing is actually SDC.

Fwiw, I did make it on an earlier flight, but by SDS as usual as real SDC was not available (including the JetBlue and Southwest flights ).