Blood doping, according to wiki, goes back pretty far and although it was outlawed the year Greg Lemond won the TdF in 1986, it has as we know been going since then...
Blood doping started in the late 1960s but was not outlawed until 1986.[37] While it was still legal, it was commonly used by middle and long-distance runners. The first known case of blood doping occurred at the 1980 Summer Olympics in Moscow as Kaarlo Maaninka was transfused with two pints of blood before winning medals in the 5 and 10 kilometer track races, though this was not against the rules at the time.[38] Cyclist Joop Zoetemelk admitted to receiving blood transfusions during the 1976 Tour de France, where he finished second, although he claimed that these were intended to treat his anaemia rather than enhance his performance... (wiki)
Would it even be possible to determine if an athlete used blood doping in training, even if not in the actual event, which I imagine would provide an advantage.