I have heard that Security will need to be done again as some aspects of the security clearance have changed since you guys went through in 2002, there is also a time limit from application to employment if a medical is required again and from memory I think this is 12 months.
Unfortunately, instead of waiting for a start date it may mean waiting to hear when your next interview is and than onto medical/security again. But I'm sure it will be all cool for you guys fingers crossed.