Forty odd years back,we had two controllers from Maastricht join us on different phases of our cadet course.The first one,an englishman,Mike L, was on the licence course,and the second,an irishman, Jim C, was on the area procedural or area radar course,but not,I think, both. I imagine that they were moved around various cadet courses to do the different stages required to acquire a CAA licence and ratings,without having to go to a unit for practical experience between each phase as the rest of us ab-initios did.Of course,this was a long time ago,and things are bound to have changed,but it would seem that then at least, a foreign ATC licence and ratings were not just 'rubber-stamped'.