That is what is likely at play here. As far as that black light test- in any case where a child is found murdered, the coroner will check for signs of a sexual assault. There were several reasons why the black light was used- first, the dissection of the vagina showed bruising, erosion and all the other indications that something had penetrated the vagina. Then there were blood stains on the panties, which of course was seen first, as they were removed before the autopsy. Those blood stains gave the coroner, and anyone else in the room, a good indication that there was a sexual aspect to the case. So, though there was no blood visible on her body, there was blood internally and on the panties. That would make someone think she'd been wiped down even without the black light. When it was used- at first LE and the coroner though it might be semen- testing showed it was JBR's own blood. This indicates to me that there WAS blood there. Just because it was no longer visible doesn't mean it wasn't there.
I feel it was wiped before the size 12s- because you can't wipe her pubic area while the panties are on. If you removed them and then SAW the blood stains, you'd get yet another (clean) pair to put on her...UNLESS the panties needed to say Wednesday. And we've explored that option already.
See, I believe she bled a lot more than those few "areas of red staining" indicate. To me, those areas represent what may have oozed out AFTER the stagers wiped her and thought she was "clean". I just feel they never saw those stains. If they went to the trouble of wiping her down (which I don't think any intruder would have done) they wouldn't leave blood-stained panties on her, even if the stains were small.