To repeat the above, with MU always, always give your FF at checkin and check your BP as it will show the right ST level you are at, along the with your number. MU always wants to assign a flight to a spanking new MU FF #. While MU is much better than they were a decade ago in actually getting mileage to a partner, save your BP.
It is amazing the number of discussions I have had in China over the years with agents amazed I did not want to credit to MU's program...