Indeed. This will in fact make a very interesting example and something you can observe on spots of cat fur as well. For a 8 cell organism which have identical twin the probability of having two twins exactly the same in terms of X in activation will be 1/2⁸. Now put it on context of an orgnisms with over 10 trillion cells! So identical twin sisters would become unique just be sheer randomness of X inactivation. Thanks for adding this valuable comment. Really appreciate it.