His rationale was comparing monthly sales to monthly sales, that would not make a valid comparison. The Aviator did not sell a single unit in September of 2006. Hence any MKX sale is an added sale.
Not trying to quibble, just bringing some clarification to jobu37's post.
I'm sure some prior Exp/Avi/Mar owners went to Edge's and MKX's. But to take off straight sales from straight sales as was jobu's post, it has to be counted both ways.