I felt the same way, and I bought mine NIB.... and there were no instructions whatsoever, other than the pictures on the outside of the box
. I was scratching my head too. Do you mean the two strips of shelf liner that are attached to the infant body pillow/toddler head pillow? As best I could figure out (and I asked here also at the time, and got the same answer), they just run up over the top of the carseat backrest, to hold the pillows in the proper place. I think I was able to tuck the ends under something, maybe the edge of the cover, in back of the seat. Since my DD was only about 6 m.o. when I bought the insert, the pillows had to be fairly low down for her, and a length of that shelf liner material was exposed -- looks sloppy and unprofessional, but apparently that's the way it's supposed to be. I think I actually downloaded the Radian 80 instructions at the time, to see if they had any additional nuggets of information about the insert, but I don't remember being impressed, LOL. Another poster suggested tucking the strips through an unused harness slot, but my recollection is that that didn't work out (I think even the highest harness slots are lower down than where you want the little shelf liner strips to go).
ETA: If you're actually using the pillows as infant body pillows near the bottom of the seat, I don't know what you do with the shelf liner -- maybe just tuck it out of the way somewhere ??
Katrin