An affirmative answer to these questions entails haecceitism, according to which the world could differ non-qualitatively without differing qualitatively. So, if the alternative history described above where Double replaces you is a genuine possibility, it is a maximal possibility—i.e., a total way the world could be—that differs haecceitistically from actuality. Similarly, if it is possible for twins to swap their birth orders while leaving all qualitative matters unchanged, that maximal possibility also differs haecceitistically from actuality.