I see how that could be argued. But, my thinking is that Tom Riddle was a student when he asked about the Horcruxes and he had asked about the number 7 specifically. I find it hard to believe that he would have not had all 7 Horcruxes made before the night he attempted to murder Harry. I don't think Rowling would throw an 8th at us by some mistake of Voldemort's death curse and inadvertant transfer of powers, etc.
Good point.
Quick correction: only six Horcruxes (ouch, that really, really ought to be Horcruces) and the seventh bit stays in Voldie. I just don't think Harry is one, either.