Call 1P and have them transfer to MP and ask for original credit. As the reroute is due to MX delay (involuntary reroute), they will give you credit right away. I just did that couple days ago (1K line though) when my 11/26 NRT-TPE flight was delayed for 15 hrs. They put me on a CI flight instead. I called in and they just updated my record in 2 min.