Originally Posted by
nineworldseries
Incorrect in my experience. I've been upgraded to F at T-72 several (4-5) times this year already, and then SDChanged into F seats. I've never downgraded myself through SDC; it's never even allowed me to pick Y seats.
You can also select a new flight and pick seats before you confirm on the new flight, so you'll know whether you're in F (you will be) or Y.
Reporting back, this is exactly what happened. It showed SDC available, I clicked on the new flight and the seat map popped up for me to choose a seat at the F cabin. I chose my seat and only then hit "Continue" to finish the SDC process. I am all set on my new flight in the F cabin.
Thank you all for the experienced responses, this is why I love this forum.