How about we declare:
1998 and before: the "open" era. Recognise that doping was widespread and the deterrence of drug testing was of limited use. No change in results as they currently stand.
1999 to 2012: the "void" era. All results null and void, for all races. This is the transition era. Again, recognise there is widespread doping and let's not pretend only those who failed a dope test doped.
2013 - : the "controlled" era. This marks a clean break from the previous "doped" years. I'm not sure how drug tests are currently done but needless to say it has to get much more strict; random tests throughout the year, samples kept indefinitely for re-testing in the future, immediate lifetime bans, all training methods and chemical intake declared etc.