A dart there (and I've put a dart in that spot on every bodice I've ever draped) can be drafted out to produce a flat pattern piece; there's no reason to leave it in. In the portraits where you clearly see the diagonal seams at the from and back of the shoulder, what you do not see is a seam at the top of the shoulder. I believe that it is a separate piece, sewn to the front and back of the bodice. We'll see how that theory holds up when I try to make the real thing. :)