Well... what I think they mean is that most carpets out there are for the Coupes and do not have the extra material required for the Fastback cars to cover the rear cargo area. Some places advertise that 'rear' piece a seperate item you need to purchase along with the regular set.
I have yet to buy a new carpet for a II (I need one for my fastback) but have bought carpets for other rigs of mine from ACC (auto custom carpets) and have been very pleased with them.