Clarify which stock should be included in data

[DaveBathnes]

In the stock summary dataset, it isn't completely clear which items of stock should be included in the exported data.

https://schema.librarydata.uk/stock-summary

Query: I've filtered it to just items with status 'available' - they could be on loan or reserved, but it won't include any that are 'deleted' or 'missing'. Do you think that needs clarification?

Suggested change

Adjust the definition to guide library services that the definition should include stock that is publicly available. This should match the policy for the items that display on the online public access catalogue.

Also include a relevant example of the problem (e.g. those that are missing or awaiting deletion) in the potential problems section.