MU REALLY, REALLY wants to assign a MU FF# to your booking. When I book the flights on MU's website and input my DL or FB #, magically at checkin it is still never there - but a new MU number is.Just give them your card, check to make sure the number status is on there and in about 5-6 days it will post. Still, always save your BP until they post.5 years ago 50% of the time you still needed to send the BP's to AF or DL - now, generally it still posts.. Interestingly, CZ is a problem still in my experience on DL, but on FB the miles post the next day. Very strange, but AFKL and CZ do have a JV.