To add to Esther's posts, I recently found this variation. Not sure if it's new to everyone because it's easy to overlook the boring Harrahs card.

The front border and completely different back variances are obvious. How about the 2011 and 2012 dates on the back bottoms? Check your dupes if you haven't noticed this. May there be other variations (i.e. 2012 version of the bordered key)?