The Model 84 stems from the Model 81 - which was 7.65mm (.32ACP) and had the open top slide, wooden grips, DA, 12 rd mag, ambi safety, changeable left/right side mag release, optional mag safety.
Model 84 - as above, but 9mm Short (.380ACP) + 13 rd mag.
Model 84BB - as above, plus loaded chamber indicator + firing pin safety.
Model 84F - as for 84BB, plus triggerguard shaped to take weak hand finger forward + hammer decocker in the safety.
Hope this helps out a bit.