It's been a while since I read Dr. Lee's book- but I have seen where it was said that the tape wasn't that sticky. As if it had been used on something else first and pulled off to be used on JBR, as opposed to being torn from a roll. Something about the edges being cut vs torn, maybe.
There was also mention somewhere about tan cotton fibers being found. That's where the Amercan Girl Doll connection came in. JB had such dolls. Those dolls have soft filled bodies made of a tan cotton. Only the head, neck and limbs are vinyl. There is a round cord that wraps around the neck and ties the doll's head onto the body. Sometimes this cord gets in the way when the doll is being dressed or when brushing the doll's hair. The Pleasant Company, who manufactured the dolls, recommended parents put a piece of duct tape over the knot in the cord to keep it down flat.
The garrote could not have come from this cord- the doll's cord is much shorter, and a different type of cord. (round, vs flat nylon of the garrote). But the tape could have ONLY if the Rs had indeed put such a piece on JB's doll. The dolls do not come with the tape.
It'd be interesting to have known if any of her other American Girl Dolls (she had more than one) had tape on their necks. If they did, we can make a pretty god guess where the tape came from.