There are some interesting results for subjects with small centres.
For example music:
5,698 entries (2019=5,848)
10.8% A* (2019 4.5%)
I think that it has gone up a lot because a lot of schools, both state and private, only put a few candidates in, so they got their CAGs. This meant that for the schools with over 15 entries, there would have been a lot of pressure to keep the grades down. One local school with 7 candidates pretty much got their CAGs, including an A* and an A even though last year they got nothing over a C. Another school which is known to be much stronger for music got worse results because there were 16 candidates.
I think this may also be what happened to DS1's friend whose A in politics was moderated to a D. Of 12,846 taking the exam with Excel, 1,012 or 7.9% for an A, 14,090 students in 2019, 994 or 7.1% got As. If a significant chunk of top grades went to the small cohorts, and they were restricting the grade inflation, that would explain the ludicrous results at DS's school.