From the T&C:
Elite Qualifying Miles or Segments will be credited 4-6 weeks after travel
...
To be eligible, qualifying travel must be posted to the Mileage Plus account no later than December 30, 2009.
I presume the latter clause refers to the regular flight activity posting, not the bonus miles or segments. It's still sort of ridiculous. They're basically saying, "If we miss or botch posting flights to your account during the promo period, you better get us to fix them quickly!"
Or maybe the clause is to preemptively admonish anyone who might forget to provide their MP number? Seems unlikely for anyone who's already conscientious enough to use this promo.