If the engine has EGR check the valve function and control system.

Also, properly check and understand what the timing is relative to spec. You may have to short a couple of leads on the diagnostic connector to get a true initial timing value. Look on the emission control decal or get a shop manual. The timing is supposed to be measured as part of the test and recorded on the report.

Retarding the timing will reduce NOx since it reduces peak combustion temperature, and the CA inspection places no limit on how much the timing can be retarded from OE spec.

I doubt if there is anything wrong with the catalyst given the low HC and very low CO.

Duke