Taking with a grain of salt but the guy at my gamestop said if you reserve the slim DURING the promo dates and don't get it until after the promo ends, they'll still honor the promo trade in prices since you technically pre-ordered during the promo.
I can see that as being a guy just talking but if it is store policy then no worries
the problem with this is that the Gamestop computers handle promotions. I doubt the computer will handle a situation like that well.
I'm also doubtful the current TIVs will last until the end of this promo. I certainly hope they do