if i use the zork adapter to slide the lens to the left, then slide the camera to the right, am i not back where i started, in which case what is the point
No, the technique is absolutely correct and it works.
An exercise to try with the camera/lens on a tripod:
a) set up camera and lens (in neutral shift) and place two objects that are in perfect alignment with the optic axis (line of sight).
b) shift lens to the left (on the camera body). Note that this is the same as moving your line of eyesight 12 mm. The two objects that were in alignment are now of of alignment.
c) shift the camera body to the right by the same amount - notice that the camera's lens is now back in the original position - the two objects will now be back in alignment in the viewfinder/LCD.
All you have lost in image coverage is 12 mm + 12 mm of the entire width of the scene (for full shift each way). For a 24 mm lens, this loss on the edges is completely insignificant.
The beauty of this approach is that the problem of parallax shift error is completely eliminated.
Glenn