One time I was flying AA EWR to TUS with a stop in DFW. They couldn't get me in the same seat all the way through so I was issued separate boarding passes for each of the two segments. In DFW I didn't get off the plane; I simply went to my new seat. I figured something was amiss when, shortly before departure, the gate agent came up to my seat and confirmed who I was. Anyways, the mileage for the EWR-DFW segment posted a few days later. It took about a month or two to get the remaining mileage posted.