That's making the extremely unreasonable assumption that tests for steroids are 100% accurate. They are not. Also, for the purposes of the count to trigger stricter testing, "no sample" was counted as a positive.
But football has testing! :D Which basically goes to show that either (A) testing is ineffective enough that you'll never know for sure who is using steroids and who isn't, so you'd better make your peace with that; or (B) it is possible and relatively common to gain those proportions without...
There will be no asterisk, and there shouldn't be. The term, after all, just comes from being a record of what happened. Those home runs happened, and that's all the record books should reflect. You can then apply whatever other history you know when discussing them, but the record is going to...