NGK told me the numbers themselves were not any sort of indicator if authenticity, the manufacturer of the fakes could just as easily buy a real plug and use any or all the numbers he said which makes perfect sense to me anyway. How the numbers were applied (stamping, etching, engraving, etc) may be an indicator but he would not get into the nitty gritty. Now fakes are becoming more of an issue it is simply safer to shell out a couple of more bucks per and buy from an authorized dealer, pretty simple solution for peace of mind I'd say.
Originally Posted by Amkeer
So NGK confirmed with me based on numbers and marking on the plugs. The numbers were the specific giveaway. For us it was immediate upon viewing the condition of the plugs. I have never seen plugs so bad when I took them out as these. All 6 were in the same condition. I ordered the set for my Tundra on NGK.com.