I had the same thing happen to me a few years back. They explained it to me this way....
We 'run the tape" late Saturday night-early Sunday morning and it is after this that they will be reflected in you account. If you ask me this is another reason why DL has lost me and quite a few of my friends. I stopped flying DL when they announced their decision to chabge SWU's. I am now a UA PE (Star Gold) and will be a 1k by the 1st week in December.
DL just sent me a mailing saying "we have noticed you are not flying with us like you did." hehe They have this right. I still have about 350K skymiles (after giving away quite a few tickets) and I can say UA is the best product on the market today and they offer F-class!!
Just my $.02
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UA PE, NW Gold, DL Gold