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A butterfly pattern was named for the shape of the nose shadow but that's not the only thing which defines it. It's more important trait with regard to defining the 3D shape of the face is the diamond shaped "mask" pattern of highlights it creates on the raised parts of the forehead, top of cheeks under the eyes, top of chin and ridge of the nose.
In skylight the pattern is subtle, which is likely why you have never noticed it, but it is there. The downward moideling directional vector of the skylight is evidenced by the fact that when subject and photographer are both on ground level looking at each other the brow of the subject will shade their eyes. That's the #1 defect in most outdoor shots I critique. What creates that shadow? The fact that the downward vector of the skylight is brighter than the omni-directional ones.
Again you are getting tripped up by some narrow definition of the term "butterfly" as meaning there's a well defined nose shadow hanging down. Again I invite you to take a subject outdoors in open shade at noon, face then north and have them nod their chin up and down. You'll see the light in the eyes, not not. Once you can see that cause and efffect in open shade try the same thing in sunlight. There will likely be more bounced fill from the ground around the subject hit by the direct sun, vs the open shade, but you'll see the same cause and effect in the eyes: chin down / eyes shaded, chin up/ light in the eyes. That's the critical factor. The fact the downward vector or the lighting all is creating a 3D "mask" pattern on the face, albeit a faint one, is a bonus.