> Key facts: students are always ranked and graded on a curve. Student populations have a fixed number of grades awarded every year, etc.

I'm pretty sure that's not correct, please find a source suggesting that. There have been major reforms (primarily the changing A Levels back from the modular version that Labour had previously introduced) and these were specifically aimed at reducing grade inflation. If there were a fixed number of grades each year there wouldn't be any inflation to counter.