I have no first clue how these people get around yearly inspections; I've assumed that particulate filters must not be covered by inspections, though it wouldn't surprise me at all if it turned out people bribe their way through. While the overall levels of corruption in Poland aren't high, the levels of respect for car safety regulations and traffic rules seem pretty low in this country.
I guess it's a symptom of the only people willing to be learn to be a car mechanic and do inspections being part of the same group which generally see emission/safety regulations as being overburdening
I doubt that. Vehicles with a DPF have an indicator of when they're going through a regen cycle.
So it doesn't require a lot of people circumventing emissions to cause damage to the environment.
The information I read[0] says that a non compliant car emits about as much NOx as 4 complaint cars. I would be shocked if your figure was anywhere remotely close to true.