Z1 has extra cores that they have already modified on the shelf. When you buy a set of turbos, you will receive one of these sets. The core that you return will be modified later and sold to someone else. The reason you can send them in first is because some people don't want to have $200 tied up for a couple weeks. The $200 core charge makes sure that you either send in your cores or they have the money to source another set of cores.
