Did anyone know about the "2007 reverse" being minted on 2008W MS coins?

I just logged into my account to see how my most recent submission turned out. I noticed that NGC had "Rev of 07" listed under the mint mark. I called NGC to get a better description of what that meant. To my surprise I learned that the mint has used some of the 2007W reverse dies in making the 2008W MS coins. NGC states they do not know how many have been made and the US Mint website doesn't state anything about 2 different reverse imagines. This MS silver eagle could be the lowest and the most expensive minted coin. My question is this.....have any of my fellow collectors found very many of these rare MS coins?