For at least some subjects, eventually what will matter is what they know, not their exam grade. If, for instance, they want to do maths at university (other subjects might be more forgiving tbf) but they haven't covered all the A level course, giving them good exam grades because they've had to self isolate, or missed some school, or for whatever reason, is just setting them up to really struggle. I think it's important, in all the talk of fairness, not to lose sight of this.
Maybe there should be some intensive summer school stuff, particularly for those moving from school to uni or college, to prevent them struggling because of this? Though that doesn't, of course, solve the exam grades problem.