I have been looking all over the internet for this information. My 2012 Chevy Volt is a late 2012 model numbering in the 20,000’s of production.
I have a hunch that GM put 16.5 Kwh batteries from the 2013 year in some of the late 2012 Volts. I believe mine has the larger battery. I consistently use 10.6 Kwh before it is empty. A 2012 Volt should only be 10.3 Kwh. I have seen 10.8 and as low as 10.5 Kwh on occasion. It also takes a bit longer to charge, like a 2013 should be.