To put it in practical terms:
I bought a quiver of Waroos in 2006. I used them for 4 - 5 years. When I finally landed my (very used 12m) in a tree & replaced it with a 2010 Best Nemesis - a "high performance" kite, fancy graphics, fancy materials (cuban fibre), elaborate bag etc. It flew like shit. It was so bad that I replaced it with a 2009 13m Waroo & also got 2009 9m & 7m Waroos. They were not that dissimilar from the 2006 Waroos - they were built a little stronger, had a better high end, but correspondingly worse low end.
In 2014 I bought Best Cabos to replace the smaller Waroos. Very different style of kite - more specialized than the Waroos - quick turning, wave kites, with good high end, poor low end, not very good for jumping. Not exactly an "improvement", but different. I now have 2013, 2014 & 2015 Cabos in different sizes. They are all very similar in performance with minor tweaking to the bridles & panel layout that are barely noticeable in practice.
Best did "improve" the inflation system, going from a basic, traditional small nozzle on the 2013's (which worked perfectly well), to wide inflation nozzles on the 2014's, which apparently had some issues, so changed a little in 2015, which still had issues & then changed again in 2016. I should say that I have not experienced, so far, any of those issues, but just an indication that kite companies tend to continually "upgrade" their products ... so that they can claim they are "improved" in their marketing releases. Frequently, these upgrades don't work out particularly well. This is not particular to Best - it's something that has occurred with most kite brands. The most important upgrade generally is new graphics so that everyone can SEE the kites are new. This is similar to the way things work in other sports industries: skis, snowboards, bikes etc.