What stops other people from duplicating someone else’s restricted keys?
Restricted keys rely on legal protection from Patents and Design Registrations to prevent others from manufacturing the keyblanks. Before anyone is given access to the keyblanks they must enter a distribution agreement which does not allow them to cut keys without proper authorisation.

How long does a keying system last?
The intellectual property protection can last up to 20 years from lodgement. In practice, most mechanical keying systems are due for replacement after 5-7 years in use; this is a result of changes to requirements and losing or tracking of keys whereabouts.