When multiple references have an identical author (or no authors) and publication year (or no publication year), include a lowercase letter after the year. This lowercase letter is also included in the reference entry.
Use only the year with a letter in the in-text citation, even if the reference list entry contains a more specific date.
(Robertson & Dowling, 2019a)
(Robertson & Dowling, 2019b)
(Dowling, n.d.-a)
(Dowling, n.d.-b)
Robertson, L. & Dowling, M. (2019a). The relevance of libraries in the 21st century. Pan McMillan
Robertson, L. & Dowling, M. (2019b). Public library programming. Pan Macmillan
Where there is the same author for different information sources and no date:
Dowling. (n.d.-a). Early literacy and public libraries. Penguin Books.
Dowling. (n.d.-b). Early literacy and public libraries. Penguin Books.
(Robertson & Dowling, 2019a)
(Robertson & Dowling, 2019b)