It is DAMN NEAR IMPOSSIBLE to get caught with EPO. You have to be a fool or extremely unlucky.
It takes 1-2 days to be undetected in your body so you could used it up to 2 and if you want to be ultra safe 3 days before competion and come out smelling sweet as roses.
The test is only a deterrent to those (who would cheat) who are worried about a random test or who don't trust what their agents/chemists tell them about how it works.
We all know that Marion Jones was using EPO, and who ever got tested more than her? She never came up positive on a test. Her supplier Conte has said you will never get caught if you don't use it within 2 days of a comp, and in most cases one day is enough. 2 days is more of a security blanket for dopers so they can relax and not worry.
It's only been those so paranoid that they couldn't race well without constant use of EPO or who were just morons who got caught. If you are summoned for a random test, you have up to 3 evasions before a penalty is enforced. Think about that!
The progression in the world times of the half marathon and marathon are due to the massive movement to them and the money they offer. They are still soft in relation the the 5K and 10K times. There is no proof that EPO is not being used, and finding proof is next to impossible unless you deal with a fool. The top runners would not be working with foolish agents or coaches.
Again, not saying that they ARE using, just that the EPO test is like saying there is such thing as a radar gun so you better not speed down the highway. Well we all know how that works.