SDC permits routing changes, SDS does not.
Yes, I'm aware. I should clarify.
My original fare bucket was not available on the nonstop flight, so I would not have been able to SDS to the nonstop at all. However, when I called the GM line at the time, a supervisor was able to force open a slot in my fare bucket on the nonstop, thereby allowing me to SDC to the nonstop instead of being able to do nothing. I suspect this only happened because one of my connecting flights was overbooked.