A and O levels are marked differently now. Don't know when the change happened, but I think it was decades ago. Grades used to show how you did relative to everyone else who took that exam, and now they show whether you reached a preset standard, regardless of how everyone else did.
Back in the late 70s when I was at school, the Exam Board might decide that the top 8% of candidates should get A, next 20% B and so on.
So if it was a tough set of papers one year and a candidate got 65%, but that was in the top 8% of candidates, that would result in the award of an A. Next year, if the papers were a bit easier, a candidate who got 65% might not be in the top 8%, so would get a B.
Nowadays, as I understand it, it doesn't matter how the rest of the field performed. Every single candidate could get 65% and if that's judged high enough for an A grade, every single candidate will get an A grade. Alternatively, if the Exam Board has decided that A grades will only go to those who get 70% or over, nobody will get an A.
This means it's easier to get an A now than it was back in the 70s and probably much of the 80s.
Also, of course, teachers now teach far more to the test than they did. They and their schools are judged on their exam results, which didn't happen back in the 70s. Teaching standards are undoubtedly higher than they were in some ways. Back in the 70s poor teachers could stay in post for life. No Ofsted, no performance management, no classroom observations, parents kept at arm's length so they would have little idea of what was going on. That's all changed, and a good thing too, but on the flipside teachers have a lot less freedom to teach more than just what the students need to pass exams. It seems to be more about drilling them than teaching them to think. That's a loss.