indication of the sources

Very soon, in 1586 and again in 1589, revised editions were published with corrections by Caesar Baronius along with indications of the sources on which he drew, and in 1630 Pope Urban VIII issued a new edition.

This was due to its absence of indications of the sources, the rare mention of divergent opinions, and the lack of provision to meet new cases, owing to its neglect to establish general principles of universal application ("Or Adonai," Preface).

The most important thing to accomplish in attributing information to anonymous sources is why we believe the information to be credible; it's incumbent upon us to give some indication of the sources' authority, with some sort of explanation for why they didn't want to be quoted by name as well.