If there two or more entries that have the same author (or authors in the same order) and the same date, place them in the reference list alphabetically by the first significant word of the title of the article or chapter. Then assign letter suffixes after the year, e.g., 2019a, 2019b.

Blau, P. (2017a).

Blau, P. (2017b).

Council for the Advancement of Standards in Higher Education. (2019a).

Council for the Advancement of Standards in Higher Education. (2019b).