Going through Elkhart in late winter or early spring, I usually see "next year" models stacking up for delivery in February or March, with deliveries to dealers starting soon after. So for some manufacturers, 2016 model year started at least as early as February or March 2015. Last production of 2015 models would have been late in 2014.
The trade show is early December, usually. Prototypes or pre-production show models of 2016 line would have been at the 2014 show. This December they will be bringing 2017 model year, for sales in 2016. The RV industry model year is thus almost a full year ahead of the calendar year, for some of the major producers.
The model year for automobiles (and motorhome chassis) is regulated to a particular window, and if manufacturers exceed that with early introductions they might have to skip a model year. This is all about what production goes into calculation of CAFE for the model year. RV manufacturers are not so regulated.
Not every manufacturer plays it this way, particularly not those who sell direct rather than through dealers.