This topic gave me a realization. Not stating that it's true, but what if Clow was Sakura's father and he wanted her to be protected, and knew that he would not always be there to do that, and maybe he knew that there were many different worlds, he would find one world that another Sakura lived in and make it her destiny to become the Cardcaptor. And because Yukito had magic, he would create a counterpart in Yue and that might also be where he got the idea for the mirror card! This is just a theory on me.