Of course, you could show percentage scores in the tests rather than where you sit in the country. That means that it should be consistent over time, although I agree that in a decent sized national subject it's probably fine the other way.

My main objection to giving percentiles relates to the OP's concern that there's no such thing as a 'very good' A, At least with UK school exams, I think that getting 100% in most subjects tests for conscientiousness and not making silly errors at best and being well-trained in the exam system at worst. I am pretty sure that if percentages were public I'd have had to get better marks to get into uni, but also that in making sure I did so I would not have been using my time usefully.

What I think would be far preferable to a 'who managed not to screw up a single question' model of getting better than an A would be an extension paper that was genuinely challenging and couldn't be straightforwardly taught.