Originally Posted by findark

Assuming the "normal" case where the premium fare component was delegated to Economy because of the single-cabin aircraft, yes you should be entitled to a premium seat if there is a change of gauge assuming your original booking class (Z in the example) is available. It takes a call and sometimes HUCA to get an agent to do it though.

Originally Posted by jsloan

If it's ticketed as a through fare -- which it normally would be, and which is why you're seeing the same prices either way -- you are absolutely entitled to a seat in the first class cabin if your fare class comes available. Anecdotally, you may need to HUCA a couple of times before you find an agent who understands the situation.

Less clear is what should happen if they don't open seats in your fare class -- for example, if you're booked in Z but they open it up as J6 C0. My personal feeling is that you should be entitled to waitlist for Z class, which is possible in SHARES but which I'm not sure all agents would know how to do. This should also get you preferential treatment on the upgrade list at the gate (you should end up in PR-1).