This doesn't help if the married segment inventory doesn't actually exist which is the root of posters problem. Both ITA and an aa.com search suffer from same problem when trying to use multi-city to specify a particular routing for which there is a covering through fare and it attempts to merge the segments under one fare. The fare search only looks at individual segment bucket availability and ignores married segment bucket inventory which is what applies to the fare availability. If your connections are long enough or they are not valid routings for a single fare, there won't be an issue as the segment can't be merged. It's also not an issue if the married segment availability happens to match the inventory for individual segments. I did a detailed demonstration of the bug here -- Unavailable Routing. (aa.com was quoting a G fare when no G bucket inventory existed on married segments as shown on ExpertFlyer). Married segment inventory is not an optional thing that you can choose to ignore. When ITA Powertools/bookwithmatrix uses an API interface to pull-up a fare on an airline or OTA website, there is no bucket inventory checking done at that point. It's just pulling up whatever fare it's told to pull up. It's only when you go to book that an actual inventory check is done and the fare quote is discovered to be bogus.