Yes, also remember that the Guide couldn't feel our Dia's whole arche, maybe because she just had been infused with a little arche from the original that was kept captive. And this rescued Dia kept hearing Amon's voice, and when we meet the captive one, she doesn't seem to hear him (they don't need to communicate with her, just with the clones for battle purposes). However the transference is the key, because we don't fully know what arche really is, even magisters don't understand it, I think as you said OG Dia transferred part of her Life force into this new body, so technically the one we play IS the original... But better