Join Date: Apr 2012
Location: Vienna, Austria
It is implied that it must have been made around the massacre, because when Perturabo says he made another one, Forrix immediately asks: "On Isstvan V?" So it seems he is very sure that before this moment, the second one did not exist. And Pertie does not contradict it, merely says it is on a Night Lords ship.
But Vulkan seems unlikely to me, because aside from Ferrus (dead) and Perturabo (busy) he is the only superior Primarch craftsman, and thus would be simply too valuable to throw him into a Labyrinth and forget him. If the traitors have him in their hands, I dont think Horus would relinquish possession of him to Curze to play with him. He'd damn well keep him and try to get him to make toys for the traitors.
If it was anybody elsethan the VIII Legion, ok, I would also bet on Vulkan, but not those who are destined to spend the next years on the back end of the galaxy playing tag with the Lion.