I don’t think it was purely copyright protection. While some other works feature SH (one involves the author’s Mary Sue being married to him), they usually show him as a cunning detective. This one is very unflattering of him, having Naruhodo constantly correct his dorky, inane predictions. Even if they wouldn’t technically have a case, the Doyle estate might act in a retaliatory way to them as they have done in some prior occasions.

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At the end of the game, it’s revealed Sholmes is really very clever, but acts in a foolish way to help inspire Naruhodo’s investigative confidence. Still, this doesn’t affect the marketing and brand impression much since it’s revealed so late.