Incorrect biblatex APA-7 citation when having multiple same author/year entries

Question

I noticed that biblatex is incorrectly creating citations when there are multiple references with the same first author and same year - when using the APA citation style. Specifically, it lists more than one author even though only the first author's last name and et al. should be used.

A short example:

\documentclass[a4paper,twoside,11pt]{report} %openright
\usepackage[onehalfspacing]{setspace}

\usepackage[style=apa, backend=biber]{biblatex} %maxcitenames=1

% Bibliography file
\begin{filecontents}{biblio.bib}
@article{entry1, 
    author = "One Author1 and Two Author2 and Four Author4 and Three Author3",
    title = "Title 1",
    year = "1993",
}
@unpublished{entry2, 
    author = "Author1, One and Author2, Two and Author3, Three and Author4, Four",
    title = "Title 2",
    year = "1993",
}
\end{filecontents}

\addbibresource{biblio.bib}


\begin{document}
\textcite{entry1} \\
\textcite{entry2} \\
\printbibliography
\end{document}

Results in the citations shown below, which incorrectly list three author names. However, APA-7 specifics that references with three or more authors should only use the first authors last name and et al.

Answer 1

To correctly implement the APA-7 style it is important to set the parameter uniquelist=false:

\usepackage[style=apa, backend=biber, uniquelist=false]{biblatex}

If this option is used, the citations will be correctly formatted, only using the first author name and numbering the years:

Note that it is NOT sufficient to set the maxnames=1 or the likes, as uniquelist=true will override these parameters.

Answer 2

While APA style normally wants just the first author + "et al." for works with more than two authors (https://apastyle.apa.org/style-grammar-guidelines/citations/basic-principles/author-date), APA style requires that more names be added in case two citations with different author lists would abbreviate to the same short form (within the same year. See https://apastyle.apa.org/style-grammar-guidelines/citations/basic-principles/same-year-first-author.

In your example biblatex-apa needs to go up to the third name to make the two lists

Author1, Author2, Author3, Author4 1993

Author1, Author2, Author4, Author3 1993

distinct. Because "et al." is always plural, the last name in each list, "Author4" and "Author3", respectively, is mentioned in full.

Currently

\documentclass[a4paper,11pt]{article}
\usepackage[style=apa, backend=biber]{biblatex} 

\begin{filecontents}{\jobname.bib}
@article{entry1, 
  author = {One Author1 and Two Author2 and Four Author4 and Three Author3},
  title  = {Title 1},
  year   = {1993},
}
@unpublished{entry2, 
  author = {Author1, One and Author2, Two and Author3, Three and Author4, Four},
  title  = {Title 2},
  year   = {1993},
}
\end{filecontents}
\addbibresource{\jobname.bib}

\begin{document}
\textcite{entry1}

\textcite{entry2}

\printbibliography
\end{document}

gives

This is correct behaviour according to APA style.

It can be turned off with uniquelist=false,, but then you would not longer be using proper APA style.

Generally speaking, if you think you have found an error in the biblatex-apa implementation of APA style, you should report this issue at https://github.com/plk/biblatex-apa/issues.