Which sources could check each verification field

Deprecated — use GET /end_users/verification/coverage instead. Get, for every field the verification response carries, the sources that could check it, best authority first. A constant rather than a fact about one submission: it says what the product can verify at all, which is why it takes no end user. A channel the submission stated through is never one of them. The form, the customer's own rows and the broker's submission are the claim under check, so they appear on a field's check with their value and nowhere here. An empty list means no run can ever verify that field.