That is a question that still needs to be answered. Its possible the sticker was initially on duct tape, but perhaps with all the water, exposure to elements, it detached and wound up on the cardboard matting? It is described in the evidence reports as cardboard matting....and I think once the heart-shaped residue was detected on the duct tape, the instruction went back to the scene investigators to see if they could locate a heart shape sticker, and this is what was found. Not to say, there could be more than one. I don't believe I read that it was definitely determined that the sticker found matched the residue on the tape??