I've been caught out on one point related to the SDC process which may be applicable in this case:
http://www.continental.com/web/en-us...romoCode=A1631
The first rule says "The itinerary must be wholly operated by Continental**" - I've been told I couldn't make a SDC on a LHR-EWR flight before because on the outbound I'd flown EWR-DUB-LHR, with DUB-LHR on BD.
Of course, common sense would indicate that this shouldn't apply when the flights are on CO/UA but you never know.