There is no difference in the frame between 2012 and 2013. 2012 is when they came up with the latest design. I suppose it is possible there were some minor changes from things they learned from the 2012 model.
I had a 2012 Giant Defy Advanced 2. Love it. But finally the weird sizing got to me and I got a 2014 Specialized Roubaix with an SL 4 frame and Ultegra 6800.
Basically the L frame size on the Giant was always a little too smal and the XL is too big. But that bike rode amazing well and steering was telepathic.
The 58cm Roubaix SL 4 frame fits me better but i find the steering is not quite as good. takes a little more pre-planning and effort.
I do miss the Giant but not because my hands fell asleep after 25 miles or so because it was too small. They need to have more increments between sizes. never doing the S, M, L, XL again and I was leery of it to begin with.