This isn't capacity.

The parent used the example of 2024s usage being X and 2025s being x+y.

So this shows us what y is.

But the precise mix that supplied X no longer exists, due to closures, so something must have back filled that x. So is that pro rata from these figures?

Yes I understand this isn't strictly capacity, but in practical terms, wind turbines and solar panels have been installed to allow this increase.