[YodasLuke]

Whether it's an Elbow Plane or Turned Shoulder Plane, we're always talking about the Clubshaft angle. The following Image of Ben Hogan indicates that the Clubshaft angle at Impact points to the location on his side where his right elbow would touch.





So, regardless bobbing or swaying, it's the clubshaft that defines the plane.

To be more precise....

Although they are great pictures, they are worthless for proving anything about the Plane. The camera is not "On Plane". So, the pictures are poor views of the geometry. Only with a camera's eye "On Plane" can lines or conclusions be drawn.

Homer - TGM:

2-F
(6th Edition)
Regardless of where the Clubshaft and Clubhead are joined together, it always feels as if they are joined at the Sweet Spot – the longitudinal center of gravity, the line of the pull of Centrifugal Force. So there is a “Clubshaft” Plane and a “Sweet Spot,” or “Swing”, Plane. But herein, unless otherwise noted, “Plane Angle” and “Plane Line” always refer to the Center of Gravity application. Study 2-N. Except during Impact, the Clubshaft can travel on, or to- and – from, either Plane because the Clubshaft rotation must be around the Sweet Spot – not vice versa.
(7th Edition)
Except for Impact, the Clubshaft is an acceptable Visual Equivalent for both Planes - especially if the Clubface is Turned "On Plane".

So, the travel of the "Sweet Spot" defines the Plane. The line drawn on the Clubshaft at Address does not define the Plane.

Zero Shift, as I understand it, is the "Sweet Spot" traveling on a single Plane.