Being helpful in the context of making the retro claim go through. I just wanted to emphasize that operating carrier really can't help that much, besides confirming they have traveller on file as boarding the flight. I have found that worth while though, because you can then act with confidence when talking to A3.

In the case of operating carrier claiming traveller was not on the flight, I've found it unlikely they are wiling to do anything. If you were a member of their FFP, they might be persuaded to do a good will act.