Originally Posted by
WineCountryUA
Yes you can use SDC but not until you get to LHR. SDC can not be used on itins that still have non-UA operated flights to be flown.
I disagree from personal experience.
I was flying LAX-NRT-BKK, NRT-BKK on ANA and was offered LAX-SFO-NRT-BKK, the NRT-BKK on a different ANA leg. This offering came straight from the UA app.