According to Nixon's Economy, the 1998 book by Rice University economic historian Allen Matusow, Laffer chalked up Schultz's eager embrace of his model to asimplemisunderstanding.
While I would have preferred to fly to England and go rummaging through the Parliamentary Archives to confirm this personally, I had a deadline to meet, plus I am not especially welcome there anymore because of what I see as asimplemisunderstanding as to whether their reading rooms are clothing-optional.