I think that, ideally, any of Yamaha's built-in voices use a different sample for each possible note-- at least for the notes that exist on the instrument that was sampled. What I mean is that, for instance, a standard piano has 88 notes, so if Yamaha is going to sample a standard piano then they can sample each of those 88 notes, but they can't very well sample the notes that don't exist on the standard piano. For most other instruments (guitars, basses, horns, reeds, etc.) the range of notes that can be sampled will be even less than 88, depending on the instrument.
Furthermore, for each note that Yamaha samples, they probably sample multiple versions of that note based on how softly or loudly the note is played.