Re: They don't rely on drug tests for past use
Indeed, and for Top Secret and Cryptoclearnce, they go back a long way. I think it's normally about 10 years for anything "Secret", but I remember getting my clearance they went back something like 20 years but I was 21 at the time.
Disclaimer: That was about 50 years ago and I only had the clearance for 3 years. Even so, they probably still have that file on me.