2009 Ten Pence Mule, Reverse of 2007

[VickySilver 775]

Noonan's sold this coin yesterday (the 2009 10 P mule) and wondered if anybody knows more of it. This is not heralded the way the 1983 2 New Pence "error" has been but evidently is much rarer - at least I believe this to be so. Do any readers know differently? When I googled it, I found only the London Coins specimen which had a scratch and one other reference that I have now forgotten. Was there any alloy change or other way of descriminating the 2007 vs. 2009 mule coins? 

And what would be the explanation for the mule, becuase I would have thought there would be more specimens out there if it had been a wrong reverse die. I think I remember reading that one of the 10 P coins had been found in a specimen currency "Anniversary" set or some such. I would think this coin would get a lot more attention or "play" as kids say these days...

[VickySilver 775]