May be yes, may be no! Are the plugs PK20PR-L11?
Aside from poor quality artwork on the packaging, the 'tell' for the counterfeit NGK and Denso plugs is typically that the center electrode is not iridium or platinum. They appear to take a conventional nickel alloy tip and machine it to look like the fine wire tip on the iridium / platinum plugs, that is where they save the money on production. The down side is that nickel alloy with a really fine tip is going to erode like crazy in use. Take a magnifying glass to examine the center electrode on the failed plug. If it is really worn down with very limited use, then you are probably dealing with counterfeit spark plugs.
The Denso PK20PR is a resistor plug. I have never experienced this; but, I would expect that it is possible to have a manufacturing flaw which results in a bad connection or no connection of the internal resistor . Unfortunately, testing a resistor spark plug with a conventional resistance checking meter is problematic. NGK provides information that suggests that the resistance of the sparkplug (from terminal to electrode) can be between 2000 and 7000 ohms when tested. However, other spark plug vendors use stuff like silicon carbide ceramic for the resistor which is highly non linear. When you test with an ohmmeter they look to be open circuit; but, when you do a high voltage test they work just fine. Denso provides no advice on testing their resistor plugs. Unless you have access to a high voltage source to test the plugs on the bench I don't think there is a reliable test for plug operation.
Your spark plugs could be counterfeit; however, if $100 was the price for just the plugs (no shipping) that is $8.30 per plug and there are a number of big name vendors that sell the sparkplugs for less than that. JEGS and Rock Auto list the Denso platinum for $5 or less. If you had paid $3 per plug, I would say that is suspicious. At your price, its not obvious that they are counterfeit. You may just be the victim of a bad production run. Is there any evidence that the spark plugs might have been dropped at some point? Dropping a plug on the floor, particularly a resistor plug should result in its quick trip to the garbage can if you want to play it safe.
Given that you have had two failed spark plugs in this batch of 12, I think a plan to replace all of them would be a good plan. Buying the plug from your Honda dealer is not a guarantee as to the source if the dealer sources the plug from a local supplier. If the plug comes with the Honda part number on the box, then the source is probably good. Buying from a big name vendor like Rockauto is also not a guarantee that you won't get a counterfeit plug; but, generally the bigger name vendors have solid supply chain relationships with the name brands so sourcing is less of an uncertainty. Rockauto appears to ship to Europe. Less than $50 for a set of 6 including shipping.
