If the huge panties were not on jonbenet until her death then they must have been taken from one of the open xmas packages. After the jab and wiping and decision to redress her. What i can't figure out is why there is blood on the pink gown and white blanket but no urine on the blanket. Was the blanket taken into the wine room at the same time as grabbing the panties but still before the strangling? It's mind boggling. If any adult staged even one aspect then they are capable of much more. It wouldn't suprise me if the blanket and gown started out as staging and even the scream and scraping sound heard by neighbors.
One explanation could be that JB was flipped from her stomach (urine stains on the front of her clothes) to her back when placed on the blanket in the WC. It is possible that the part of the blanket that was pulled over her torso simply did not touch her body closely enough to get wet. I agree the panties likely came from a package in the basement- Patsy did admit she bought them as a Christmas gift for her niece but did not get around to mailing them and said she planned to do so when she got back.
The blood on the nightie is more problematic. She did NOT bleed from the head bash. She DID bleed from the vagina. It would be helpful to know exactly where the blood was- and was it a smear, splatter or just a few drops.