most of the font comes for the most complete sound board, ie the CF which uses more boot sounds for instance (randomly selected at boot time)
the pre-on (preactivation) sounds are sometimes provided with alternate sounds for the user to "tune" the sound font to his taste, the bonuses are just copied in the font, or renamed to replace certain sounds.
IIRC, the NB uses only one boot sound, but the prizm probably 4.