Normally, "Freight" on an airliner goes into the "Hold" - normally under the floor through a large cargo door, or two, each big enough to accept normal freight pallets.
Freight does not normally get onto the Passenger Deck.
Normal Cargo Doors are normally mounted on the Left (Port) side for normal airline loading/unloading operations.
Tristars were only normal to begin with but were modified to not being normal by being capable of outsized freight movement - and C17's can do that now.
I would imagine that the big doors and the passenger decks were only used as a normal routine because they were there and someone had paid for the equipment to lift things up and put things through the door.
Most the "Freight" I saw carried on Tristar Decks could have fitted into baggage holds but the equipment to load them effectively didnt appear to be available at all stops?