If Mary can conclude about there being a drug which conan uses to revert back to his original body, then she should also be able to know that the drug's effect is temporary. In that case, snatching one capsule from him is useless unless Masumi intends to play the snatching game again.
@Sherlock2020 remember way back when Masumi send Conan's photo to someone and that someone replied back calling him a wizard? That someone was shukichi. So yes, he does know who Conan is. But i wonder whether he knows anything about aptx.
@wakedonia now that you mentioned it, each of them do so but unless you can say that about all the new cases released I don't think there is any hidden meaning to them.