Several people have already posted links to the RVIA info on this, so I'm not going to do that again, but ALL states SHOULD be using the RV manufacturer's model yr designation, not the chassis yr. Some DMV employees don't do it that way, but they are WRONG, and those RV registrations SHOULD be corrected. Ferndaleflyer; your situation could result in less money in your pocket when you go to sell, albeit probably not a huge difference.
For what it's worth, my current RV is a 2004 model, built in 2004, on a 2004 chassis (that was built in 2004)...so there is no question; DMV agrees that it's a 2004.
However, my last RV was a 1988 model RV, built in 1988 on a 1987 Ford chassis (that was actually built in 1986). DMV registration correctly lists it as a 1988.