Not mileage, but dollars.

Twenty-five years ago, or so, I flew SLC-LHR-SLC on a combo UAL-TWA ticket. Fare was $1,012.

A few months after the trip I wondered why the charge hadn't come through. Going back over several months of my Amexco statements I find that it had indeed. The charge was for $10.12. Being the honest fellow I am, I wrote a letter to Amex. They said take it up with UAL, who had issued the ticket. Wrote another letter, never heard another word about it.