In short – yes they do. Constant stretching permanently expands the material, not by a lot, but since wetsuit should be snug it is noticeable. This is the most visible in places where there is lots of stretching – for example shoulders on a wetsuit without a back zip. Besides the stress put on the neoprene the material also ages, especially if it is exposed to the sun. Older neoprene becomes stiffer, less flexible.
Stretching the neoprene.
So what does that mean? Should you get a bit smaller suit and then stretch it out? No:)!