A RV Manufacturer buys trailer components at B to B pricing and almost always in a large quantity. The same for motorized motorhomes (Class A, B, and C). It is not all uncommon to have a 2015 motorhome riding on a 2014 chassis. Ditto trailers. Many of the components (refrigerator, furnace, water heater, etc.) will have manufacturer dates older than the motorhome or trailer.
The situation can get interesting when emission laws change. Your 2006 chassis may be under a 2007 motorhome, but the emission laws of 2006 apply. Note: there was a change in emission laws for diesel engines between 2006 and 2007, and the issue was discussed frequently at that time.
2013 Flagstaff 8528IKWS, 2006 F-350 6.0L