similarly my first sent stamps FI-1 to china has not been registered. the member did not sign in since june ! i know he is active in another website, just does not bother to register i guess... well, it would not be a surprise though if mail gets lost to china, or chile, so it may be they really did not receive.
i dont know also why the members who dont even sign in for months may be at higher ranking -especially as he has only sent once and there are others who have done the same later but still are after him in ranking...