Back to the what years were big changes thing. Lots of subtle changes over the years to get to where they are now. Here's a summary off the top of my head with regard to the 2 stroke 800:
2012 - First year of the proclimb chassis. Wasn't any lighter (maybe even heavier) than the 2011 M-series. Had less horsepower too, but much better suspension. Fit and finish was rough for a new model. Riding a 2011 M8 back to back with a 2012 the 2012 didn't do anything better off trail in my mind, but was smoother on the trail. Painted tunnels and skids on limited models.
2013 - Change from 40" ski stance to 38", 2.6" lug track replaced the 2.25" lug, front skid mount location lowered to make the sled feel lighter on its feet. Short cooler with painted tunnels and rails on limited models to reduce ice buildup on tunnel and rear suspension.
2014 - 26 (?) subtle changes from the 2013. Highlights include rear skid relocation down and back (same location as current sleds). Change in clutch heat treatment to minimized warping and belt heat generation. Short cooler and colored tunnels/skids extended through the snopro package. A bit lighter.
2015 - largely the same as the 2014.
2016 - Change to Team brand clutches greatly improved durability. 36" ski stance with revised spindles and castor angle (still used on current sleds). Revised rear skid geometry (still used on current sleds). Limiteds got Evol shocks and 3" lug tracks. Switched to 7T drivers for more track clearance, but left chaincase gearing the same so they were geared too low overall. Changed to Borg Warner chain and gear profile for greater chain case durability. Skis that didn't sink to china, but were really twitchy IMO.
2017 - Mountain Cat model was added to the lineup - Same as 2016 Limited but had 1" narrower running boards and belly pan plastic pulled in to reduce paneling out on side hills. Also first model with the lowered driveshaft and back to 8T drivers propelling the track. Bit lighter. Front suspension geometry, tunnel, bulkhead, and skid geometry the same as current sleds.
2018 - Ctec motor. Refined, slimmer body work. Deflectionless Team primary clutch. Upgraded shock package on Mountain Cat model. Aluminum driveshaft and reduced weight. Re-designed skis.
2019 - Added the alpha skid/track option. Factory tether. Nicer handlebar controls. Re-designed skis again. More HP.
With enough time, money, and parts you can make anything back to a 2012 into a 2018 with a Suzuki motor.