Hi. There are many different types – different designs – of Nauticats. The early ‘Classic’ 33 models didn’t have a raised aft deck, but the later all glass fibre 33 and 331 models did ..or rather, do.
But other models – of similar lengths to those “cruising” motor-sailors – were designed as specifically *SAILING* yachts, rather than 50/50 motor-sailors. The keels vary between models, and the sail plan varies between models.
It’s like Fords. There are many different models of “Ford” cars, although they all have the name “Ford”.
With a bit more specific info, you should be able to look up the differences online, but with just the generic info ‘1984’ and ‘1991’ ..that isn’t sufficiently detailed, sorry, to give a better response.