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Actually the grroves obove the top ring are a wearable surface for lack of a better word. It is to reduce surface area in that area should the top area contact the wall when the piston rocks over center. That surface does not come into contact with the wall, but in old days, before there was skirt rigidity and geometry, they would cut grooves like that in the skirt as well as the top area of the ring lands to prevent galling. I suppose now its there just for tradition. All the Wisecos I get have that.
The groove between the two top compression rings is not for a third comp ring, it is there to give the oil on the walls a place to go as the top ring wipes down. It helps avoid a hyraulic lock between the top rings. The top ring actually controls the oil contrary to what you think, the oil control ring gets most of it out of the way, but the top ring is what really does the job since that is the one that seals tighest against the walls.
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