Stack and reach are static unless the lower headset stack and/or the fork length are changed. For a given frame, fork, and headset, stack and reach do not change.

For over a century, getting the contact points (saddle, handlebar, and pedals) in the same relative position from frame to frame by adjusting saddle height and setback, and stem height and extension was all that mattered as far as riding position was concerned. Nobody had ever heard of stack and reach the way the term is used today.