It appears that 2009 is the first year for the 31TS. If it was an automobile, you'd tend to stay away from the introduction year. I don't think that the RV industry is quite that sorted out. It might come down to little things...I'm willing to bet that the LCD TV is bigger in the 2010 following the trend with other camper year over year.
Nights camped in 2013 - 55, 2014 - 105, 2015 - 63