No.
You really have to define what a "level playing field" actually means.
if you think about it, is it fair play if one player or team finds a training method that gives them a clear performance advantage, is that not in the spirit of competition ?
Why do we merely restrict it to the pharmaceutical side of training ?
One thing I will say is that cycling is has long been the whipping boy of the PED debate.
One could argue that PED's are banned so that competitors don't HAVE to use them to win, this would not be the case with a completely free market/open slather interpretation of that "sporting chance" really means.
Let us not forget that many of these drugs can and are harmful to your health, and of course open to misuse and abuse.
Birds, to answer your question, in many cases there was nothing to stop you from using PED in your training previous to major events.
This is no longer the case with very thorough random screening systems in and out of off season.
For example, I believe cyclist must declare their intentions to return to competition at least 6 months out from the entry date.
This is so they can be monitored and returned into the testing schedule to prevent the situation you have described.
Now, for the drugs themselves, Obviously as you would know through your studies many have various chemical half lives or "glow time" as it is called.
This is the time the drug is detectable within your system/piss.
Using cycling as an example, I know that the testing for synthetic EPO has become much more advanced even over the last 10 years, but still teams found a way around it (as with US Postal and their microdosing technique)
It's also interesting to note that the drawing and re-infusion of blood samples is completely undetectable, how the hell can you ever prevent this ?
Where is Terry in all of this ? he would be the man to ask.