Just a thought, but who says Castle didn't formally allow the use of their SCL?
I couldn't find any direct reference of that in the article, except for "It is hoped this will address the messy issue of the split caused by Castle and RISCOS Ltd developing their own separate SCLs, as this new module from ROL is intended to be compatible with software built for the Castle SCL."
I remember an article about such a dispute between CTL and ROL about it. I believe Castle did offer them to use it, when certain conditions were met. For details, see -