That's a nice explanation, makes alot of sense. I made up this one theory where soul in Nero's arm is the same demon that attacked him (somehow the demon's essence was placed in his arm) and if we assume that that demon is Vergil, then it'll explain how the order was able to find pieces of his armor (he somehow ended up in Matis Forest and went on a rampage), the demon attack on the town (again, Vergil on a rampage), and gives reasons for why Vergil's soul is in Nero's arm (reasons meaning that it was intentional, I don't believe he's searching for his body, I think he was actually trying to escape from it, which is why he is in Nero's arm and allowing him full command over his soul. Its understandable that his will would be incognizant but then you have to consider that in DMC1, at least to me, his defeat wasn't a "oh I'm dying" moment, it seemed more like he was finally breaking free of his curse, which could possibly lead to a split between his soul and body, but this is all mere speculation on my part)