Not very "strong" speculation considering that Epogen, the first synthetic erthyropoetin (EPO) drug, was approved by the US FDA in June 1989. Before that, Epogen was not commercially available. Do you think bike racers in the 1980s built a biotech lab and created their own synthetic EPO, or got themselves sick enough to enroll into clinical trials of experimental drug?
but was EPO available in Europe or elsewhere? The FDA often takes its time approving drugs/devices that become available outside the US earlier. It may have also been available via "clinical trials" before general release. That being said, "strong speculation" means bupkis.