An interesting video of the Tesla Model S sedan's evolution over the years has been put together by the people over at Black Tesla.
The 2013-2014, 2014-2015 (with Autopilot hardware) and latest 2016 version were examined.
From the detailed exterior and interior walk-throughs we can chart dozens of changes.
Also the quality of the cars has improved overall with each new versions, which is especially seen in the decreasing size things such as body panel gaps.
Black Tesla says of the mini-documentary:
The Evolution of the Tesla Model S (2013 - 2016)
The Evolution of the Tesla Model S, looking at documented and undocumented changes over time. A guide to understanding differences between the different model years for Tesla Enthusiast and prospective Owners looking to buy New or Pre-Owned.
NOTE: I did not have access to the 2012-2013 Model S nor the 2015-2016 Model S. Key elements not represented are Leather appointments in the 2012 model and the introduction of the heated steering wheel in the 2015 model.