That was also the point just before the VW scandal proved that diesel engines can be high-mileage or low-polluting but not both at the same time. Which is why diesel VWs are rather less common today.
Mk4 VWs are MY 1998-2005. There's still a heck of a lot of them on the road now, but I think the peak was probably well before 2015 when the "scandal" took place.
