I love Anderson Silva. He was legit my favorite fighter, maybe even more than GSP. However, it's likely Anderson Silva just didn't get caught. So many people don't realize that you can be doping and still pass 80% of your drug tests, or more if they're scheduled tests.
People on these forums don't really understand how PED testing works, AT ALL. They think if you take PEDs and get tested, that you'll just pop. But these fighters are smart: a lot of them have inside information when they'll get tested, or they play games with the whereabouts for random tests. They have all the time they need to take masking agents to throw off the tests.
I would say, ballpark, a "doping" fighter is only going to get caught on maybe 20% of the tests -- and that's random tests. For scheduled tests, they just cycle steroids and have everything well out of there systems. The only exception there is metabolites which store long-term, like Turinabol. And again for metabolites, there's only a small % chance they'll actually get detected.