Chardy
O level exam boards did their own thing, hence some were letters, others numbers. (All CSE grades were 1-> 7. Grade 1 was O level equivalent, 1->5 a CSE pass)
GCSE was supposed to pull it all together, hence every exam board was A->G.
It changed 9->1 so that in few years they can easily stick another number on the end!
Remember these changes are rarely (never?) made for educational reasons, but political ones
GCSEs were originally introduced to combine the two tier O level and CSE systems, nothing to do with the different O level boards, which were all A-E by the eighties. The idea, we were told, was to have every sixteen year old taking same exams so that no one felt the "stigma" of taking CSEs. They were graded A-G and all grades were considered a pass. It was all a nonsense from the beginning because everyone only considered A-C to be passes. Until very recently, there were also different levels of the exams according to the ability of the candidate - as had always been the case under the old system. Then, of course, the standards of the exams became more like the old CSE rather than O level, which meant that the brightest candidates were not stretched enough and grades started to rise exponentially, leading to the introduction of the A* grade. The introduction of numbered grades in 2017 was the Emporer's New Clothes. With all this being said, I sincerely hope that anyone here whose children or grandchildren received their results yesterday have achieved the grades they needed.