The Smog Test(s)

I've been enjoying supervising a water pipeline replacement project a couple of blocks away. I don't know how they could do it without me?
I finally got Lou's car smogged, after 5 tests. It's evidently considered a high risk car due to age, so it was sent to a "Test Only Station." I don't think there is any difference in the test, just that the Test Only Station is supposed to fail you so you retire the vehicle. Note, the car is an 87 Volvo wagon much like our "Toad". It runs great, and has been extremely well maintained. It's low mileage as well, only a little less than 300,000 miles.
The car failed the smog test for high NOX, every thing else was normal to low. The first test was 980, it needed to be 730 so I asked our mechanic where to take it. Seemed like the repair needed to be at a shop that was allowed to do the repair and had a tester. Our mechanic recomended a shop down the street. The mechanic there looked at the test results and said, we needed a new catalytic converter. For $250 we might pass, for $400 we'd be sure to pass $400 got us a real hungry catalytic converter that just loves NOX. I went for the "pass for sure" repair. The test on their machine said it was good (630), not as good as I expected but OK. I took it back to the test only station for a retest. It failed worse than before, now 1400, twice what the test just 30 minutes before was at the garage. I took it back to the mechanic. He consulted with our Volvo mechanic and the test now passed his machine twice as good as it did on his before (350). Another trip to the test only station and this time it passed even better than at the mechanics (250). Went dirrectly to the AAA to get the tags. Done!! Three days, $105 for tests (60, 30, 15), $400 for repair, no extra charge for the second repair. Sure sounds like a conspiracy. They just wanted to know we wanted to keep the car.