I'm scheduled to fly DCA-IAH-FLL tomorrow because I need the segments. I'm departing in the afternoon, and I'd like to do an SDC to an earlier departure. I'm currently booked in W class, ticketed as a standard one-way booking.

When I look up flights on the app, there's an earlier departure with the same routing (UA 697, DCA-IAH, connecting to UA 401, IAH-FLL), and the app indicates that L class is available on the first leg and K class on the second. Both have W. However, when I try to make the change through OLCI, the option doesn't come up as a same-day change (a couple others do).

I called United, which told me that only Q class is available. In fact, the app is currently only selling the flights I want in Q and U classes, respectively, and not, apparently, as a married segment (even though it's one of the options for DCA-FLL).

Is the app showing phantom fare-class availability? Or is the agent not sufficiently experienced with SDC, and only going by the fares for sale? Or has United changed its SDC policies to prohibit agents from going on per-segment inventory?

I don't know how SDC is currently handling broken fares, but that pairing is a Q/U fare for a new ticket, and I suspect that's why you're not getting it as an option, even though the married inventory does indeed include W for both segments. Agents should be able to make the change, as such. However agents seem more and more inexperienced in my current experience, and as a front line they basically use the same website you do, so it may take some trying before you get one that understands what's wrong and what needs to be done to make the change.

The agent is correct � the lowest available inventory is Q..

This is partially correct, but your conclusion is wrong.

Yes, the app is essentially showing phantom inventory. That�s because the target set of flights is available as a married pair � you can see the inventory in ExpertFlyer. However, United�s pricing engine is willing to insert a fare break on a connecting itinerary when attempting to price it. It does that when the price is lower than the corresponding through fare. When that happens, Expert Mode shows the individual, �divorced� inventory for each flight. That inventory is not available for a flight change. That�s why the agent isn�t able to do it.

OP: Try using the regular flight change tool, instead of the SDC flow, and use multi-city search. It�ll require changing your existing flight to DCA-IAH, and then clicking the �Add flight� button and adding IAH-FLL back in. I can�t promise anything, but this might get you access to the same inventory you�re seeing in expert mode.

Alternatively, since you�re already booked on that same routing, you should be able to standby. Assuming that you clear the DCA-IAH leg, you should be able to SDC the IAH-FLL leg after boarding.

Thanks for pointing that out, I hadn't noticed expert mode was behaving that way. So expertflyer is the only way to see the true married inventory when the search is giving a fare break?

I�m not aware of any way to tell UA to exclude broken fares from its pricing search, so, yes, probably.