Chassis model years run change in autumn (October through December) of the year before what is on the VIN. This is regulated Federally. Thus 2019 chassis won't be built any earlier than October 2018, maybe not before December.
Finished RV model years change late winter of the year before, i.e. January or February, to have new model examples for the Louisville RV Show. Manufacturing of 2019 motorhomes might thus start February 2018, building up stock for Spring and Summer sales. There is no regulation of this.
Thus half to three quarters of motorized RVs might have a finished vehicle model year at least a year "newer" than the chassis model year. RV manufacturers stockpiling the chassis compounds the problem.