Really hard to tell. The Denso info is also not very helpful (I think it relates to an iridium plug, given the shape of the electrodes). Looking at the word "DENSO" engraved below the hex nut, your spark plug is obviously fake, but so are all other 4511 spark plugs sold online (including Rockauto). So that cannot be true either. Even the suspicious little dent in the ground electrode seems genuine compared to the pictures at NAPA and Autozone.This very interesting. Thanks for looking this up for me. I took a spark plug out and it seems to pass all the tests I gave it including the scratch test, scrutinizing the ceramic portion and electrodes, letter indentions and packaging.
I would try to restore the situation when you only had the Coil C circuit error and proceed one-by-one. So first put back in the old coil (next to no work). Then put back in the old wires (little work). And if that doesn't make the power return, finally the old plugs (most work). If you don't have the old plugs anymore, you might buy a cheap set of copper plugs from a reputable source. Ordering them online (as you know we have a little discount at Rockauto) in stead of buying them in a shop makes it less likely that you get plugs that were "returned" (me suspicious?).