Which data sources does this use?

Three, kept separate on purpose.

Google Search Console for impressions, clicks, position, and query-to-page association. Raw server request logs from my own server, parsed and classified by crawler vendor and stated purpose. On-site structure: schema coverage, machine-readable endpoint validity, internal relationships, indexable surface.

They are not merged into one score because they answer different questions with different limits. A server request proves a request reached a URL. It does not prove indexing, a search, a citation, or a human reader.