I am proofreading a text where two authors are listed (one of which is the writer, and the other, apparently, only a "supervisor") and in reporting the author(s) use first person singular (instead of first person plural): I believe, I was surprised etc. I find this very illogical and was wondering whether there was a rule for this type of situation.
To be more specific: right below the title of the essay two authors are listed. However, in the introduction and in the conclusion, the author(s) say that "I was somewhat surprised..." and, towards the end, "it is hard for me to..." It seems illogical to me to list two authors and then report in the first person singular. When I suggested this be edited, they told me only "one person was the writer, while the other one was the supervisor".
What should be done in such a situation? Should the "supervisor" also be treated as one of the writers and verbs be written in plural, or should this person simply be removed from the list of authors regardless of his or her contribution?