I think the Hasselblad 500c was introduced in 1957. The older lenses for 1000F/1600F indeed had round apertures with many blades. In fact the five blades is the Thing I dislike most about Hasselblad and Rollei lenses from the 2nd half of the century, though Hasselblad had round apertures at least in the 110/2 and 150/2,8.