Correct spark plugs and correct torque are needed for proper spark plug indexing. Another member of the forum stated that incorrect indexing can lead to the plug actually being eroded by the high pressure fuel because the injector can spray directly onto the tip of the plug.
Just another thought.
I can remember years ago on a Honda 750 putting a paint mark on the spark plug metal shell lined up where the metal electrode attaches , and the idea was after torquing down the sparkplugs, I did not want to have incoming air fuel blocked by the back of the ground electrodes.
I also remember F'N up and setting the valve lash in thousandths of an inch instead of hundredths of mm and wondering why the engine sounded noisier than normal