Lois Potter's commended edition of The Two Noble Kinsmen "spends eleven pages . . . separating out the authors' individual contributions" before ignoring the subject in the text and notes. Is determining individual contributions useful, or is it a part of Potter’s editing style that is unnecessary if the question of primary authorship is not considered essential?

Is there an amount or type of collaboration where it would be appropriate to privilege one author over another? If so, how should an editor go about determining who deserves to be deemed a co-author and who only a minor collaborator?