I just got my copy! A lot of the GameStops in my area were sold out already so I had to go a little out of my way, but I got one. I'm so glad they decided to sell it early!
And if it is indeed a misprint on the insert, I feel like we could hit up Sony for a code if we end up not getting the pre-order costume packs. It says:
Thank you for pre-ordering your copy of LittleBigPlanet PS Vita. Use the promotion code below to access the Big Daddy, Little Sister & Knights of Old costume packs for your Sackboy or Sackgirl.
So even though we didn't pre-order the game, it still says that the code can be used to access the costume packs.