Don't really have a source ... if you look at the Giant bike archive you can clearly see from the pictures how the design changed between 2011 - 2012. On the later models the seatstays joins the seat tube at a point below the top tube, whereas on the older ones all the tubes join at the top of the seat tube. Also they moved to an all carbon fork with a larger diameter steerer (which they had initial problems with for which they had to issue a safety recall). This was around the time I bought mine, I bought a leftover 2010 in early 2012. The only thing to point to same frame for 2013 vs. 2012 are:
- frames look exactly same, and same specs on web site
- manufacturers rarely do major redesign in consecutive years, just paint/component spec
- lack of any mention of changes in online reviews for the 2013, which would tend to mention such things