I'm not sure if there is a bunk over the newer models or not. Most of the interior pictures I've seen of the newer 17's seem to have upper L-shaped upper cabinets over the sofa area, so they don't look like they have a bunk. Maybe it was an option?
Just another thought a little OT - the newer ones weigh a lot more than the older models... The X-terra is very similar to my Frontier, and although it tows the 17' just fine, I don't think I would be comfortable towing much more weight
What floor plan is your 13'? I'm always on the look out for a front dinette model....