There seems to be one other difference between the J and the Ja I have noticed and that is to the top of the gown across her left shoulder and out along her outstretched arm.
On the J there are some deep folds running down across her arm , but on the Ja the folds are almost non-existent which as you can see on the worn example I have shown lead to an almost straight line from her neck to her outstretched arm, albeit with a slight dip in the centre.
On the J though the line across the shoulder is broken by darts of the folds even clear on the worn example. First two Ja second J