I concure with George.  If CIA gave an invitation for a second poly then they must want you and want to work with you.  My experiences have all been good even through a wrongful termination investigation.  I have never liked the poly but it helped me from being wrongfully terminated in cojunction with some depositions from employees.  

I have worked along side people who have admitted drugs in their youth and not in their adult lives and the poly agreed with what they said, that they had not taken drugs during their adult and professional lives. It sounds like you are still in the running.  However, if it went to a third poly and you got asked in again.  That I could not see happening.