The JW's could very honestly and truthfully point out that biblical prohibitions against blood are all references to whole blood.
Off the top off my head, take for example isolated anethole or eugenol juxtaposition major blood components that characterize blood. Could it honestly be said that eugenol is not cloves and one could use it without tasting cloves or experiencing its effects? A legal or chemical argument could be made that it isn’t —same as with blood.
But then what do I know?
Your reasoning is persuasive. Your information is valued. Your argument also implies that since JW have been wrong about fractions then why shouldn’t they be wrong about the teaching altogether since they claim to be guided by God in which case they logically wouldn’t be wrong about the fractions. And if God is not part of the equation, it is wholly a medical decision. —But we still have the Decree and what it means for Christians. And what God meant in the Decree. Christians in good conscience can’t just pretend they are not bound by it and put anise or anethole or ethanol into their bodies and believe they are only required not to eat it or that they are allowed to by God because it is lifesaving. The Decree says to abstain from blood not JW leadership.