After they went to the new frame in 2009 there were no subsequent frame changes. It should have the larger front seat post, rectangular section seat stays, sort of square section boom tube, and some hydro forming on the top and diagonal tube as well. They have an integrated headset too. If it doesn't have a frame like this it is 2008 or older.
Here is a pic of our 2009 M/S. The frame should look like this except with a "Fatty" fork.