In the search for Truth, it helps to be able to call on friends from around the world. Exposed below is a major myth -- the 'away leaning' spine in the Backstroke. From Scotland, the Home of Golf, to your desktop, the Home of Lynn Blake Golf.
Top two pictures, something is out of whack. The backgrounds which should be static are not the same. I think the camera was moved between shots or something. The camera in one is higher than the other, and also closer.
Again there is a difference between frames regarding the background and your red line is definitely not in the same place if you use the background as a reference.
The Tom's pictures I think really give the wrong impression as well. Using the tree braches to the left at the top and his head, it hasn't move near what your lines indicate. Not saying it doesn't move a bit, but those lines make me think he is about to fall over and I doubt seriously that would be a product of your instruction.
Also the Snead pictures have questions regarding the background including the position of the ball to feet. Something is just not the same about both.
Interesting concept that the stationary head or neck would be considered a psuedo component/variation.
Realizing that the First essential is a Stationary Head, though 2-H does state it is recommended not mandatory. But when reading 1-L-1 and 1-L-2 it seems that the head is indicated and that it can move (turn) by the action of the pivot but not on its own.
So what in the Pivot would require the head to move? Wouldn't the pivot only require a turning? How can you move the head without disrupting the top of the spine unless you bend at the neck to lay the head down on the shoulder?