Ran into this last year and was not able to get any credit. I was on a United flight from AMA-IAH-DFW and was rerouted on AA to go from AMA-DFW becuase of equipment problems. I contacted both United and US Airways and was not able to get Original Routing Credit. I missed out on like a 1,000 miles which didn't end up mattering. The policy doesn't really make sense to me in that I could have gotten ORC on United but not US Airways. I mean really? Common sense doesn't always work with these folks.