Here are some things from the book and some things that JK Rowling has said that just make you think (I write my comments on it in white):

Harry does not have a godmother or another godparent - Sirius was the last, sadly for him:
No, he doesn’t (have a godmother). I have thought this through. If Sirius had married… Sirius was too busy being a big rebel to get married. When Harry was born, it was at the very height of Voldemort fever last time so his christening was a very hurried, quiet affair with just Sirius, just the best friend. At that point it looked as if the Potters would have to go into hiding so obviously they could not do the big christening thing and invite lots of people. Sirius is the only one, unfortunately. She says he is the only one... IS? Are you sure you didn't mean was, mrs. Rowling? Or is something going on with Sirius so that he still is, rather than was? Could it be that Dumbledore knows something about the mysterious veil that Sirius so gracefully fell into? I think we should all take a closer look at what Dumbledore's middle names mean... Also, JK Rowling has stated that we have not seen the last of the mirror that Sirius gave Harry. Could there possibly still be a way for Harry to be in contact with Sirius through that mirror? It was probably just JK Rowling making a slip up when she spoke, but either way, it's something to think about. Why would she slip up saying that if she wasn't thinking something to that extent?