US cars all came with dual round sealed beam lamps to meet US lighting regulations.
Outside Morth America, all cars came with the single piece lamps which incorporated a main beam, dipped beam, parking light, turn signal, and fog light all in one.
When the 6.3 was introduced in 1968, Mercedesí felt they needed to incorporate the new brighter longer range halogen lamps for such a fast car. At the time the only halogen bulbs available had a single filament, so they needed to use separate lamps for the main and dipped beam.
Rather than design an all new housing, they pressed the lamp housings and frames they had used on USA cars since 1959 into service, getting Bosch to make main and dipped beam lamps for the H1 halogen bulbs that would fit in the US housings. These became standard on 6.3s sold outside the US, and were made optional on other models.
While Mercedes was able to design turn signals that would replace one of the clear segments between the lamps, there was no room to incorporate a fog light. So cars with the dual halogen lamps will often also have auxiliary fog lights fitted either side of the radiator grill.