On a MH the coach and the chassis are two separate things that come together at the plant. It is likely the plant was still using the remaining 2012 chassis (which carries the vin number) on a 2013 coach (which carries the MH model year). This is very common because when the manufacturer decides to quit a model year production to switch over to the next, there are usually many prior year chassis not yet used. I will likely see that on the unit I have on order.
2016 Sunseeker MBS 2400R