There are ways to manufacture new varieties of anabolics (such as winstrol, deca, eq and such) so as to mask them from any sort of drug test. This however, requires alot of money (million?) to do. Basically, it will bring the ratio of the two test levels tested for to be more even... i.e., I think it is the hepi-test level... it will raise... making it more even in ratio to test levels...
Hence, a passing of a test, while still on... olympic athletes could pull it off all year long.
C-ditty