Yes, absolutely. We introduced regulations on April 1, 2004, that instituted a system of end dates or expiry dates for the 900 series, so any temporary worker coming into Canada would only be there...and it's tied to their immigration paperwork. So those social insurance numbers will cease to exist or will be eliminated from the social insurance register, and therefore cannot be used, and if anybody tries to use them, they will be flagged in our system.
On June 15th, 2006. See this statement in context.