yeah the ITAC and CRB have to be dilligent and knowledgeable enough to keep updates percolating down on such cars, but the difference in standard equipment, body pieces, etc.. would play havoc with the IT "cannot make a model" rules. best to keep them divided.
as a really good case, check the 92-95 civic and del sol in ITB. 4 body styles, all with the same engine and trans, on 4 spec lines (DX 3dr, DX 2 and 4 dr, LX, and Del sol S). the differences here are more subtle than on most of the cars in the list on post 1, yet the decision was made to be pretty "granular" in the classification. I certainly cannot see listing even less similar cars on one line GOING FORWARD, though the ITB mustang and ITS RX7 are examples of pretty mingled up existing spec lines.