I've got a similar horror story of purchasing "authentic" NGK Iridiums for my 08 TL that turned out to be duds about a year later down the road. Caused all kinds of misfires and the car ran like absolute crap. After investing too much $$ into coil packs from different brands (oem,NGK,Import Direct)that remedied the problem temporarily. I smartened up and pulled the plugs I had replaced only 12 months prior and Wallah !!! they were worn to nubs and black as soot covered in carbon and unburnt gas. I think running like this for an extended period of time played a role in my rings failing at or around 212,000m killed my motor prematurely (for a Honda at least). I'm still saddened by it till this day but you live and you learn
