To have a 2 year difference is very common with 2008/2010 RVs. The usual difference is only one year. But, if you remember 2008, there were big economic problems in the country and many manufacturers ended up with a supply of 2008 vans. (and many went bankrupt) Winnebago in particular apparently had hundreds of them. I would bet that all their rigs for 2009 and 2010 were built on 2008 platforms.
Just for your information, the Navion is not a Class B, it is a Class C that was built on a cutaway Sprinter. (Their Class B is called the Era) But that doesn't matter in relation to your question, as this happened with both Class B and Class C units manufactured in these years.
Mumkin
2021 Promaster 1500 188wb conversion
2019 Roadtrek Simplicity SRT (half Zion/half Simplicity)
2015 Roadtrek 170
2011 LTV Libero
2004 GWV Classic Supreme