Thanks, Linda, it is useful to compare some examples. They are really all over the place.
A complicating factor is the various androgynous figures. For example this one really looks like it was first a man with obscured genitals - which may be why someone drew breasts on it later.
The circle-breast is rare indeed, though I think there is one more here (top nymph):
The two in the bottom I added because they illustrate a perspective tool I was unaware the artist employed. Instead of drawing one brease "inside" the torso, it is added "behind" the one in profile. This indicates that the upper torso is twisted more to the side. Even though I had studied variations in body orientation quite extensively, I hadn't noticed this subtle difference before.