Originally Posted by acf1270

Of course I could be wrong, but something tells me that Delta IT is not going to be able to distinguish the booking date when it comes to crediting the bonus miles as long as you are registered for the promo and travel by Dec 31.

But anyway there is this sign advertising the promo in the RDU airport that clearly states "Enroll before Nov 30 and book and fly by Dec 31. So if you purchase a ticket in December and don't automatically receive the bonus miles, sending a copy of this sign in should do the trick.