Novice question but why do some early bays have them and some don't ? Is it just because they had a repair underneath in the past and they didn't refit them or are there more model changes that I don't know about.
Had a set of belly-pans on an old bay, must of got a range of holes in at some point as they filled with water that washed around and lead to the demise of inner-sills, jacking points, out-riggers etc...I would suggest taking them off to check for pond life if you have them, or if you are looking to buy a van with them on....