That's a very good question.
Every 12 to 18 months, we issue a confirmation process. We write to all the people on the register to confirm their address. If they do not reply, we take it that they have moved, and we remove them from the register. It is regularly verified, so there will not be several years before that occurs.
The other thing that is important to know is that if a kit is issued to the wrong address—for example because a person no longer resides there—a number of elements of information need to be completed on the outer envelope, which are then matched with the information we have in the register to make sure that only the right person is using the kit.