I travel often on one airline and request miles for a FF partner of that airline at checkin (flying on US Airways and reuqesting mileage on UA is one example). On occasion, I notice that my mileage does not always post to the partner and the partner claims it can take 4-6 weeks to process. Instead of going through the hassle of sending in boarding passes, receipts, etc., why can't I just give the FF center my PNR number and they can use that? Or my ticket number?

Do other FF partners often have access to these systems? I assumed they were shared. Or do these numbers disappear from the system after a period of time?

Maybe I am thinking the systems are more advanced than they really are. Any insights?