That engine does not have an EGR valve. It has variable valve timing on the exhaust valves, which accomplishes nearly the same thing. If the VVT system isn't functioning it can lead to high NOX.
What are the other gas readings from the smog test. That may tell us something.
The cat monitors will not tell you if the reducing catalyst part of the cat is misbehaving, only the oxidizing part.
Cats these days are made to reduce HC and CO emissions by encouraging more oxygen to those molecules (oxidizing), and to reduce NOX by removing oxygen from NOX molecules (reducing). The P0420 code only speaks to the oxidizing function of the cat.
NOX is not generated until the engine is under load (and thus the need to do the test on a dyno). NOX is only generated when the combustion temperatures are hotter than intended. Things that can contribute to that are EGR not functioning (not applicable to your engine), exhaust VVT not functioning (could apply to you), too much ignition timing, air fuel mix too lean. And, it is also possible that the cat wasn't hot enough. It helps to drive the car in a spirited manner for about 15 or 20 minutes prior to the test, but don't let it cool off by waiting in line for another 15 to 20 minutes.