Some more interesting points in Sam Snead’s downswing.
Upswing-
The forward press seems to be done with the knees.
The lead knee remains initially very stable and only moves towards the trail knee during the last moment of the up swing. This action is like a little booster action allowing deeper coiling to be obtained.
Down swing -
Initial move - lead knee buckles out considerably towards the target whilst weight remains on trail side as there is no lateral hip slide.
Old timers such as Joe Norwood and Paul Bertholy were much inspired by this particular down swing action typically of Sam Snead's swing.
Nick Pice, if I remember correctly, mentions in his book keeping the weight onto the trail side in the initial phase of the downswing.
The lead knee has a considerable action during the down swing. The large buckling action towards the target is followed by a substantial reverse action when the lead leg (and trail leg) is snapped straight.
Notice how the trail elbow in the down-swing is very clearly visible below the lead arm which isn't the case in the up-swing. This is indicative of a flattening of the down swing from the top.
There is a remarkable stable vertical stacking of the body during the downswing.