The letters we were referring to are, for example, letters we would get from a shelter administrator providing proof of address for homeless people. They are just used as proof of residence if those people need to register on polling day. So they are not vouched for in the sense that they've provided identification--a health card perhaps--saying this is who they are. Those letters serve as proof of residence, and then we register them.
On December 7th, 2006. See this statement in context.