The past couple RIM and monthly returns that I have done I have found at least 1 or 2 items on them that we were not issued credit for parts that we returned. I also had 1 transmission where they had charged me 17% to return it and it was authorized as s strike related return. Keep a eye on all of your invoices!
I was able to contact the PDC's involved, and I was credited, but if you don't watch you will miss something.