Can't really say, but I will anyways, but the fact that Guillermo de Toro has had the signature sheets for literally years, and still hasn't got around to signing them, (time management issue?? uh-uh) - well, don't know the real reason, but there must be more to this. How long does it take to sit down and write a few hundred or so autographs?
Wouldn't surprise me if the sheets have gotten lost...
sk