If the calibration engineer does the calibration incorrectly – or a malefactor intentionally introduces a miscalibration – then the end result would be off. Every time. Even though there was nothing wrong with the sensor data, no security breach between the sensor and emissions device, and furthermore, every line of code in the device was completely correct.
In fact, the only way to detect a calibration attack is by running an independent analog test. In other words, someone would have to get their own exhaust particulate measuring device and run tests on real vehicles to see if the emissions device was properly calibrated.