Yes, the AD3-4 rivets hold the forward part of the rib flange to the spar web under the tank skins. You can see them in this picture.
I see the call out on the plans for the AD3-6 rivets above and below the two nutplates. I just looked at my wings and those holes are empty! I guess I missed that callout on the drawing.
The note on the DWG 11 says to put the nutplates on the forward side and have the heads countersunk on the aft side. These extra holes probably need to be filled, although I can't imagine that they would add much if any strength to that area given the nutplate rivets are also right there.
You can see the empty holes on my spar here.
I will have to get those holes countersunk and filled with the rivets.