Harry hasn't been seen in four years, and of course people only check on him when the Hogwarts letters go unresponded to. ("Good evening, young Mr. Dursley. I only have a couple questions for you." "Who are you? How did you get in my house? Why is that feather moving on its own?" "Magic, young one. Now, I've already asked your parents a few questions about your cousin." "What, you mean Harry? I don't know where he is, haven't seen him in years. Can you go away?" "All in due time, my boy. Now, I know you only have one other blood relative who was aware of Harry's... situation with your family. Tell me, what do you think of your Aunt Marge?")