When I requested a credit on Austrian then the BP and ticket was not enough. They also had to verify it with OS. After 2 months I got tired of waiting and contacted OS. They faxed a computer printout "proof of travel". I am sure that US could provide similar info.

It shows my PNR, ticket info and routing. Next to the two OS flights there is a comment "FLWN".

I was going to fwd this to UA but coincidentally (?) the miles appeared before I got a chance.