I agree with the other responses. Even some of the best programs are likely near the edge of over-training. There is a delayed effect from much of training. The work you do now will likely take some time before you can reap the benefits from the prior training.
Since we don’t have anyone who can say definitively that “you need exactly this amount of work and this type of work at this point in time”, much programming is a best guess scenario. Naturally the longer you have exposure to such programs, come to a better understanding as to individual responses to the drills, volumes, rest intervals etc. the better one can make such decisions to create an even more effective program-for that person.
Of course it’s the prior training, too, which allows one to rest or taper from and achieve higher performance levels-overreaching. Otherwise we should all rest and never train to improve:).
I have experienced what you are talking about as well, where you are forced to lay off or greatly reduce your training. You get back into the gym or track or whatever the venue might be and really surprise yourself. You might go in with low expectations yet you can get very good numbers.
The down side of that, to use CF’s words, is that eventually (possibly) the gains or improvements in freshness will be outweighed by the losses of fitness. That is the further removed you are from the previous higher (though hopefully not excessive) volumes of various training elements, the less likely you will be able to hold onto those fitness levels and consequently performance.