Congratulations! You'll have fun!
I may have the explanation for the 2004/2005 discrepancy. The Class C manufacturers buy the vehicle on which they'll build the RV - chassis, cab, driveline, etc. - and then start building. Sometimes, by the time they're done building, the new model year has started. So the automotive part of the RV is from one year, but the RV itself is from the next year. Our 2007 Class C has a 2006 vehicle under it. I have to remember that when I'm seeking service. No big deal; you just need to know.