I was looking that the ATB 5 oz coins and they don t even have the last 2011 for sale yet. If they did make them in 2011 why are they waiting so long to sell them?
Someone will probably pop in with the official answer. But I'm sure if you went to the Philly Mint you would see a guy there put the finishing touches on the Chickasaw or Vicksburg coins. Of course, they might have actually struck them in 2011.
Check their product schedule link. The 2011 Chickasaw goes on sale on 2/09/2012, so another 8 days. The Vicksburg is already on sale, it went on sale on 1/12/2012.
This coin is most likely affected by special legislation that dictates how long it can be on the market. I recommend looking there for your answer.