It is less complicated than it looks, once the terms are clear.
The change has been coming for a while, but it only became obvious this year.
What it costs
The practical effect is easier to see in a single example than in a summary. The figures move about, but the direction has been the same for three years.
The exceptions
There is a deadline involved, and missing it costs more than the difference. Nobody is required to explain this to you, which is half the problem.
What to check first
Nobody is required to explain this to you, which is half the problem. Most of the confusion comes from two terms that sound alike and mean different things.
It rewards a little attention now and punishes leaving it to next year.