I've read the explanation of the serial numbers for both the "old" style formatting and the newer formatting. I looked on the back of my 12c (purchased approx. 18 months ago) and found the serial number: CNC51207503. I know the CN refers to china, the 05 to 2005...etc. What does the second "C" refer to? I haven't been able to figure this out. All the other examples I've seen only have two letters.