The date was 1 October 1988; those PPLs whose Instructor Ratings were granted before this were awarded 'grandfather rights' Restricted BCPLs.
Which begs the question... in the intervening years (nearly 18) why haven't these individuals taken the exams and done the skills tests to at least prove their skills at the professional level?
The only real reason I can think of is medical (ie. the need to hold a Class One medical to hold a CPL), but those who - for whatever reason - could only ever hold an old Class 2 medical would have been granted a Class One (with an an 'aerial work only' restriction) with the advent of JAR, thus allowing them to qualify as professionals.