Steve,
I don't know how true this is, but in my decade-plus-ago research, someone once told me that there were a few of these made for bike-shows, then the regular production that one see's in the Raleigh catalog. I don't know if the 531SL bikes were production or demo's or whether made in England or Japan...they very much look Japanese to me...but my decals are little left so no help there.
I also find it interesting that the model name, Superbe, is the same as gruppo. Sounds like Suntour and jap Raleigh had a mutually beneficial agreement to promote each other's finer offerings.
Jack Romans
Sacramento, CA