I recently reinstalled OSX, Win7 and Linux on my mid-2012 15" Retina (purchased August 19, 2012), and just noticed that I, apparently, am now running OSX Lion (10.7.5).
I recall that this machine came with Mountain Lion. I'm not sure exactly how this happened, but the only fix I have in mind at the moment is to do an internet recovery, which I hope will get the system back to ML; but, I'd rather not have to back up and restore 500+GB of Linux and Windows stuff in order to get a 4GB installer to download.
Forced internet recovery, which also says Lion instead of ML. Going to try nuking the recovery partition to see if that helps.