Certainly. When I read the last 2 books for the first time I did deduce myself that Harry could be a Horcrux himself, even though Voldemort never intended to make him one ("The Dark Lord shall mark him as his equal") but I was still unsure if my deductions were correct. When Ghost Dumbledore confirmed it, it was a kind of a euphoric feeling I was correct. If somebody spoiled it like that, it would have ruined that feeling, so yeah, it was a very bad spoiler.
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