But that's not what I see in the Stack & Tilt book. I forgot what page it is, but there is a picture showing the backswing from behind. The author drew a line in the middle of the back, starting from the waist up to the shoulder. The line slants to the left. This image, in conjunction with the straightening of the right knee, demonstrated to me as the customer that as I make my circular backswing and straighten my right leg, my spine slants to the left and I achieve the "tilt" part of the swing.
Now if I got the wrong impression from the picture and misinterpreted the instrucction, isn't the burden on the S&T; authors to provide a different explanation? After all, they are in better position to explain what I need to be doing.
Additionally, you state that Foley does indeed advocate decreasing the flex in the right knee on the backswing. But That's not what I take from his instruction. From his Golf Digest lecture on the On Demand, Foley states that as you make your centered backswing, you'll feel the muscles in your right leg contract and put pressure into the ground. When I put this into practice, my right leg ends up staying relatively flexed. And when I'm in this position, I feel like I am in a better position to make the transition from the backswing to the downswing. This instruction, along with the other ones he presents, has helped me achieve better ball striking.
Now do both Foley's and S&T;'s teaching methods actually achieve the same movement? I'm not a golf professional but if we presume Foley "stole" from S&T;, then the answer would be yes. However, the most effective method in explaining this movement to me as the customer was Foley's terminology and not the S&T; terminology.