Also, the bloodline curse in Changes and the heart exploder in SF killed in similar ways, but the ritual in SF was NOT a bloodline curse, it used a thaumaturgic link powered by ritual sex. I don't think it needs to be the same person teaching sells and the Red Court. If two coaches who have never met each other both grew up knowing the rules of football and watching the same games, it is not unlikely they will both draw up similar plays. So I don't know if the connection is necessarily there, other than Arianna getting nudged into action that involved Harry.
Where do we have evidence that 3eye is a "far advanced" potion? He did not have the "Bloodline Curse", though the curse he used did have a similar effect, it did not target a bloodline. He had a demon summoned, it is possible that the bound demon was compelled to tell him something about curses, or even potion making. Or it could have been another demon that he summoned. All of this is speculation, of course.
Changes page 161-162 for whole convo. i am just using the important piece.
Harry,"How does it work?"
Vadderung,"it tears out the heart. rips it to bits on the way out, too. sound familiar?"
Harry," hell's bells." it had been years since i had even thought about Victor Sells or his victims.
Vaderung, "it's all connected, Dresden. the whole game. and you're now beginning to learn who the players are.
the sorcerer who used the spell in Chicago before didn't have strength enough to make it spread past the initial target. the RC does.no one has used Power on that scale in more than a millennium."