That should not be necessary, on the email you should see something like mine listed as "customer changed their mind" which I guess == DSR.
As for the RMA number that is just how a medium-large sized company works, they might receive 100's of items each day so if returns came in without any sort of number on someone would have to open each one up and work out where they came from, time == money
So like the company I work at if it doesn't have an RMA number on it then it gets delayed (or in OC's case just flat out refused).
So as long as your RMA note does state the changed their mind as the reason for the RMA (Return of Materials Authorisation) then that RMA number they have issued will refer to a DSR on their files.
Good luck (probably sending mine back monday now, just hunting around for some good packaging to go around the box it came in).