It was added to the banned list after McGwire was found with it. Yeah, it wasn't illegal PED use, but he was using PEDs that are no longer allowed which contributed to his 580+ HRs. He's not guilty of illegally using them from the info we know, but his numbers can be called into question based on what he's admitted to using. ex post facto? Sorta, I'm not saying based on what we know is true we can admonish the guy, but in historical context we can lessen the significance of his numbers based on evidence that he used PED's that we know hold to be illegal. Sort of like how we give extra credit to those hitters that played in the 60's for lesser numbers in a pitchers era with a higher mound in use. Of course there's also the dark cloud of steroids use that we can't prove yet if ever. You're double counting by deducting for andro use in addition to the deduction everyone takes for him playing in a hitter's era.