I'm sure that there is some explanation to this. This question has been asked before. Why is it that some P8R heads have P8R-12, or something else stamped on them? Because some or most have only P8R stamped, and this one head that was being asked about on some forum had P8R-12 stamped on it. There was a picture of it and everything, and it was clearly stamped P8R-12. Is there a difference?