re Grade boundaries. This is my understanding, it might not be exactly right.
With 'O' levels, they were scored on a normal distribution, and something like 10% got As, next 20% got Bs or whatever. This meant that a proportion were always destined to 'fail' no matter what, I think. But an A meant you were top 10% that year.
Under GCSEs the standard is (was) meant to be absolute, so you could take the exam in any year and still get the same grade. However 'grade inflation' has meant that more pupils have got higher grades over time. Whether this is due to better teaching, or teaching to the test, or easier exams is a moot point.
If an exam is accidentally harder (or easier) then how the marks translate to the Universal Marking Scheme (UMS) is adjusted, in theory so that the same standard gets the same grade each year. However there is a school of thought that says that interference from government has sometimes meant that grade boundaries are adjusted to make things harder to pass. (e.g. English last year).
So if an exam board decides their Spanish exam was accidentally extra hard, they could lower the amount of raw marks needed for a particular grade. However if they just decide that this year's cohort just weren't as good, then they won't.