Q: A colleague is adamant about citing page numbers even if the reference is used more than once in a paragraph. Is this necessary?
A: There is a little advice on citing page numbers in the manual, just above section 3.7.
If the author wishes to cite different page numbers from a single reference source at different places in the text, the page numbers are included in the superscript citation and the source appears only once in the list of references. Note that the superscript may include more than 1 page number, citation of more than 1 reference, or both, and that all spaces are closed up.
Example: These pages showed no sign of proactive sphincteric adduction.3(p21),9
You’ll notice that it’s not mandatory and our style includes, “If the author wishes.” Page number citation can be helpful to the diligent reader who wants to go to the source cited and find the exact mention of the quoted material.—Cheryl Iverson, MA