if the car has over 100k miles, i suggest you do a tune up, fuel system cleaning.
then its up to you if you wanna try the test again or put on a new cat as well before trying the 2nd test.
the front part of the cat (called reduction catalyst) controls the nox emissions and if that part is not working then your nox emissions will increase.

as far as egr, if your car is obd2 then most of the times it will set a code if its not working.