No layer covers the entire country equally. When a value of report appears with "covers 62%", it means that this number was calculated on 62% of the surface of property: there is no data for the rest.
It is the difference between a reliable average and one that describes a part of property. A productivity index calculated over 90% says a lot; above 30%, describes a sector.
Where there is no data, it is said. It is not filled in with the average next door or extrapolated: an invented data is worse than none, because it reads the same as a real one.