Niklas shelving

I've just decided to reassemble this and am completely puzzled over the shelf supports. They each look like a shepard's crook and 2 and 2 attach together to form an arched side support - but two have holes going all the way through and 2 do not. At first I put the holed ones together but then realised the others were not drilled. I then tried to put 1 and 1 together but this is not sturdy and they fall apart. I only have 6 of the attachment bolts. You can affix to both ends of the support bars but that would mean having nothing on the other uprights. This is then wobbly?

I am completely confused as I do not seem to have any other fixings. My instructions show how to assemble shelves and cupboard and I already know that! As the shelves are solid wood the structure needs to be rigid to take the weight. Can anyone help?