Chelly - you are a welcome poster! If you don't mind, I'd like to provide some info about the size 12's, to save you having to backtrack.
There were NO OTHER size 12's found and taken into evidence by police. Sometime after the R's had been relocated to Georgia, they returned a package of the underwear, without the Wednesday pair, to police through their attorney - saying they were found in some of their things that had been shipped from the house after they vacated it completely.
Patsy was questioned about the size 12's and stated she purchased a package for her niece, during a trip she made to Bloomingdale's with JB while in NY prior to Christmas. Upon returning, Patsy was said to have conceded to JB's begging to let her keep the package of undies, saying she would grow into them. Patsy supposedly relented, and they were put into JB's underwear drawer in her bathroom.
There was also mention made of the gift for Jenny Davis (the niece) not having been shipped off in time, and PR was intending to do it when she returned from the Disney trip, along with some other items she wanted to send to Georgia as holiday items. Patsy claimed to have used a "wrapping station" in the basement, so speculation is that the underwear might actually have been laying there - maybe even wrapped, but not included with the other items in a shipping carton for later.
It does seem almost unbelievable that JB would "beg" to keep a package of underwear that were several sizes too large for her, when obviously they could have been purchased much closer to the time she would have really needed them. It has also been thought that perhaps JB wanted them, or Patsy purchased them to be used over a pull-up, as a 'camouflage' for times when wearing one was necessary. Possible - and that Patsy would not have wanted to disclose that vane action.
However, fact remains, a package that was supposedly the one that supplied the WED size 12's found on JB, was later sent to police, and since the R's were supplied with evidence lists, if any size 12's had been on it, they would have known, and NOT needed to send any others.
What is a puzzlement, as Chrishope has so well established, and also others along the way, is WHY would there be any need at all for ANY underwear to be placed on JB under her lj's if both the adult R's were colluding to cover for either BR or themselves if they had cleaned her up after a sexual attack? Why not just let her be found with the vaginal wounds (a fresh one in an attempt to mask the chronic?), since it might point even the more to an attack by an outside molester who probably would have kept a missing pair of underwear as a 'souvenir'.
IMO, the only reason for JB to be found dressed wearing a pair of undies with the lj's is because someone wanted someone to believe she was NOT sexually harmed at initial glance - that the neck ligature was the reason she was dead. This would have fulfilled the ransom note criteria of JB being killed for any number of reasons, and no reason for the 'kidnapper' to have been thought of as a sexual deviant.
As rational thinkers, it would be a given, of course, that everything that happened to JB that night would have been discovered forensically once the body was located in the house. However, if the body had been successfully removed from the house, while it makes most sense to NEVER have it found again, at least while it was intact, there would have been a chance it would be located. If it was, would it be a stretch to think that the killer wanted JB to look as if she had been strangled - in a 'beheading' sort of way - and with proper layers of clothing intact, no sexual attack?
In order for us to consider this, we must remember what several LE people commented: This was not done by professionals, there were amateur mistakes made. It was a night of horror in that household, and in that type of insanity, IMO, there might have been some very bad choices and mistakes made in assuming that the presentation of JB's body would fool someone if it was found before there was time for decomposition to take it's toll.