[Daryl]

Why does the uncocking stop at level and then held in place at level whilst the swivel into impact occurs?

Golfbulldog,
You asked the Magic question.
The Magic of the Right Forearm Question. Pass Go and collect 200 dollars. The Left Wrist is passing through its “Level” position at Impact.

Consider the Left Arm as a Rope tied to the Clubshaft at one end and Your Left Shoulder at the other.

All Left Wrist Action (Bending, Cocking, Rolling) is controlled by the Level and Bent Right Wrist and Right Elbow. From the Left Wrists point of view, it’s doing the Uncocking, but from the Right Elbows point of view, as it straightens, it Uncocks the Left Wrist. Therefore, fully Straightened Right Arm equals Uncocked Left Wrist. Following Impact, at full extension, both Arms are Straight but the Right Wrist has remained Level and Bent.

This is all in the Cliff Notes. Page 821 paragraph 16. Illustration #549, the "Swingers Release Sequence" High Speed COLOR photo's should help to understand this better.