Clarify the number of entities in each dataset

[psd]

The Local Planning Authority dataset page says there are 337 LPAs, but there are only 311 without an end-date. The page could say:

311 active, 26 historic, 337 Local Planning Authorities in total

Similarly, the [Tree Preservation Order][(https://www.planning.data.gov.uk/dataset/tree-preservation-order) dataset reports how many entities we have. This is a subset of the total number we know there in England. Here we should use our data quality framework and expectations to provide an estimate, along with the count of how many entities we have. The page could say

35,476 tree preservation orders of an estimated 500,000-600,000 nationally.

In this case the number of sources could also be imroved:

Data provided by 19/311 authorities".

Here the provision table could show the number of authorities we expect to provide data with a link to the providers service, or upcoming performance page for a consumer to dig into the details