Pagani was really established around Zonda. It was the first car to ever be produced, and since its release in 1999, there have been quite a few different versions. What I found odd though is that even though Pagani claimed to have officially stopped production of Zondas, ending with the Tricolore, is that every couple of years a new one is produced. After days of research on the topic, we found out why.
Pagani, like Koenigsegg and Bugatti, has a sort of refurbish program. If you so happened to own any Pagani car, you can request it to be refurbished to your desire. This is not limited to older Zondas, but has also been done on a couple of Huayras as well. With that said, Pagani will never stop building Zondas, or any model created after that because people can pay to have their special touches added to it.
The price is a bit of a set back however. When refurbishing your car, they recreate all the body panels, and can even add new external body parts to it. This process does not include rebuilding a new chassis, but anyways, the average cost of this process starts at around $1M and can go much higher based upon your specification. This process is kind of like McLaren MSO, a further customization of your car.
These cars are not new cars, everything is the same except for the color, and maybe the interior. So that is the reason, Pagani makes existing cars even better.