IMO in the very beginning of the NH case JVS was able to give great detail about the underwear that NH was wearing that night, Now IMO if you are in the backseat of a dark car, and then at a dark beach there is no way that you would be able to recall all of the detail of this garment, but if after you killed her you took them as a souvenir of you killing you would know exactly what they looked like...
Forward to the SF murder I think that JVS removed her pants in order to again take her underwear as a souvenir (sick if you ask me) but when he realized that it was her time of the month he no longer wanted to deal with them...Again this is just MO that would explain him removing her pants...
I also think that she had her shoes on and was in the upright position during this horrific crime and the blood dropped onto her shoes, I can tell you the forensics will show if the blood dropped from a distance of her height or if it was castoff from blood being slung around the shoes, but I still think they were on her and JVS removed them before he removed her pants.