What happens when a sex offender registry is not kept up to date?
At the link is the story of a family who moved into a home previously occupied by a registered sex offender. The registrant moved but the database continues to list the address. When the new homeowners asked to have the address removed, they were told the address would be removed if they paid $200.
This was a privately operated registry. I do not assume that registries operated by law enforcement agencies are any less likely to put people in danger.