>>7543418As a rule of thumb think of them as non-compatible. Even the ones that share the same mold (Saber 1.0, casual Saber, original Saber Lily) don't fit as perfectly as the ones included with the figure unless you force them a bit. If I remember correctly the same happens with the Sabers after the 2.0 (2.0, the two Grand Order Lily and Saber dress).
And then we have Nero. I think none of the three are compatible with the Artorias. I don't really remember if the original and Bride are compatible between them, but you can be sure Extella Nero isn't.
