It's hard to compare season to season in the recent past because our schedule has been so dramatically different year to year.
Comparing 2015 to 2014 is fairly consistent, once the season is done, because we play a pretty consistent schedule of teams (though you have to get both WSU and Army in your data before you can really compare, given how extreme their offenses are on both ends).
Comparing 2014/15 to 2013 or earlier doesn't work as well, just because of the teams faced.
2015/2014 - Ohio State, Michigan State, Nebraska, Wisconsin, Michigan, TTFP, Indiana, Maryland, WSU, Army, FCS... the only real variance is Tulane/Kansas, and the bowl opponents UNC/TBD. These are two good years to make a basis of comparison. Admittedly, there are complicating factors such as the unexpected losses of players from one season to the next [Dailey, Barnwell, Boggs, Peele, Stephenson, Hamilton (injury), Jacobs (injury), Austin (injury), Carroo (missed 3 of 7 games - 2 full, 2 halves), etc], and the suspension of Flood for 3 games.
2013 - Louisville, UCF, Fresno State, Cincy, Notre Dame, Houston, SMU, Arkansas, UConn, USF, Temple, E. Mich, FCS. There is not a single team that compares from 2013 to 2014/15. Different styles of play, different level of opponent, etc... comparing stats from one season to the next is like apples and oranges.
2012 - Louisville, Kent State, Cincy, Cuse, VTech, Pitt, UConn, Arkansas, Temple, USF, Tulane, Army, FCS. Only 6 of 13 games overlap from 2012 to 2013... and only 2 of the 6 teams that finished with the best records. While there's at least some basis to compare year to year, the majority of the schedule changed from year to year - meaning different styles/levels of play, again.
2011 - WVU, Cincy, Ohio, UNC, Louisville, Iowa State, Pitt, Cuse, UConn, Navy, USF, Cuse, Army, FCS. This is a much more normal season-to-season comparison from 2011 to 2012... 8 teams remain the same, 5 changed (usually just 4 OOC games, but this is close). The added change factor was the loss of WVU and the pick of up Temple (a pretty big difference there, which should see some improvement in rankings from 2011 to 2012 all on its own).
2010 - WVU, UNC, Pitt, USF, Cuse, UConn, Army, Louisville, FIU, Tulane, Cincy, FCS. 9 teams overlap from 2010 to 2011, which should make for a great comparison from year to year.... but the complicating factor of LeGrand's injury mid-way through 2010 puts an asterisk on comparisons.
2005-2009 are also pretty consistent, as they have a steady conference schedule plus Army or Navy (very similar in style, but not necessarily in quality).