Not only do they have changes by year but also within the same Model Year. Coachmen for example starts their changes around August of each year. My camper that was being built was coming of the line AFTER the one that I ended up with. The one I ended up with has a different colored cap, has LED lights, a white sink instead of stainless steel, I lost the pull out trash can inside and the dťcor had different options.
I think it has more to do with the final scheduling (how many left over parts they have to continue to build the older models yet the newer ones (same Model Year) have already started production as well.
2015 F350 6.7 Platinum
2015 Coachmen 360IBL