But if you kept doping at the same steady rate, especially if it were properly monitored, why would you have wild fluctuations? I suppose, if you stopped doping for a while and got tested, your values would drop suspiciously low compared to the doped baseline.
Perhaps the ones who get busted have less sophisticated operations, and screw up. It wouldn't be much different from warfarin therapy. Keeping your INR within a certain range, once treatment is established, isn't that hard most of the time.