I think that these days doping is just trying to stay in the plausible deniability (is that a real phrase?) stage. The ones that get caught are typically the stupid or those that are so obviously doping that the authorities basically have to take them down. When Ben Johnson won the 100 in the 1988 Olympics, he was a roided out freak with muscles bulging everywhere and almost glowing yellow eyes. He blew away the field and destroyed the world record. There was no way that he was not doing drugs in a big way. There are conspiracy theories that he was framed in order to get a positive, but I won’t go into that here.
Over the past couple of decades, some of the biggest doping issues in track have been with national governing bodies condoning and helping to cover up any doping. A few years ago, a number of Russian women’s middle distance runners were busted because they were all submitting identical samples of clean urine. None of it their own, of course. WADA suspected them because they never missed an out of competition drug test, which is pretty much unheard of. This would probably have to be coordinated at a level much higher than the athletes or coaches.
Greece has been known to hide their athletes in the off season, and they rarely run outside of the country, so they are rarely tested. There was the faked motorcycle accident from Kederis and Thanou before the Athens games. The reason the testing officials wanted to test them is that they had been unavailable for testing for months. Another episode happened at a world indoor championship where the testers met the Greek sprint contingent as they arrived at the airport because they had been unavailable for months. The athletes dashed back onto the plane while the coach physically kept the testers at bay.
I also highly suspect the Turkish women in the middle distances. The woman who won the 1500 today had previously been banned for a drug offense.
As for the Jamaicans, they have an incredibly strong sprint tradition. Having been to the Penn Relays, a ton of Jamaican high school athletes compete at the highest level there. They usually take almost all of the sprint relays, totally dominating the US high schoolers. A huge chunk of those get scholarships at US universities, so it is definitely worthwhile for them.
I’ll stop now.