Here's a data point. I compared membranes from a 1987 1391401 and a 1996 71G4644.
They have compatible trace patterns.
(That is not to say that these membranes are interchangeable. The 71G4644 is rubber dome, and its contacts are directly below the centers of the keys. On the buckling spring board, the contacts are offset maybe 2mm from center.)
But, from the controller's point of view, they look identical.
Next step is to compare this to a mini's trace pattern.