Well, you can still punish people if you catch them doing it by other means than sampling their body fluids. Seems like even if their is no test for some PED the PED could still be banned.
Freegards
On a practical level there really aren’t other means, I suppose there’s a chance somebody could catch them with the drug in a clearly marked bottle in their locker. The problem with banning something you can’t detect is that’s basically announcing to the athletes you govern that this substance works, since there’s at least 10 rumored things that accomplish nothing for every 1 that does something clearing that picture up for them is counter productive. MLB ran into that problem when they banned certain “cleaners” (things that remove traces of other stuff from your pee), by doing that they functionally announced that those cleaners actually work and they became very popular for athletes of sports that hadn’t gone down that hole yet.