APA cite multiple authors -- why switch order will affect the effect?

Question

I want to cite two paper, which both more than three authors in APA format. As far as I know, when number of the author is more than three, no matter if it is the first time, only the first author will be display. I am using the overleaf platform, and wondering why switch the citation order will change the format.

here is the how I cite the paper,

such as A and B
\citep{Petkov2008,Petkov2009} \citep{Petkov2009,Petkov2008}

here is how the compiled file show. such as A and B (Petkov et al., 2008; Petkov, Logothetis, & Obleser, 2009) (Petkov et al.,2008, 2009

here is how those two paper looks in the reference.bib

@article{Petkov2008,
author = {Petkov, Christopher and Kayser, Christoph and Steudel, Thomas and Whittingstall, Kevin and Augath, Mark and Logothetis, Nikos},
year = {2008},
month = {04},
pages = {367-74},
title = {A voice region in the monkey brain},
volume = {11},
journal = {Nature neuroscience},
doi = {10.1038/nn2043}
}
@article{Petkov2009,
author = {Petkov, Christopher and Logothetis, Nikos and Obleser, Jonas},
year = {2009},
month = {07},
pages = {419-29},
title = {Where Are the Human Speech and Voice Regions, and Do Other Animals Have Anything Like Them?},
volume = {15},
journal = {The Neuroscientist : a review journal bringing neurobiology, neurology and psychiatry},
doi = {10.1177/1073858408326430}
}

thank you all for the time and help:)))

Answer 1

If I interpret the (somewhat fragementary) information you've provided correctly, you're using the apacite citation management system -- likely with the option natbibapa -- and the apacite bibliography style. Do be advised that apacite implements the formatting requirements of the 6th edition of the APA manual.

If your document needs to adhere to the formatting requirements of the current, 7th edition of the manual, your only viable choice at present is to make the switch to biblatex/biber and employ to the apa style. (There's also the apa6 style which, I'm sure you can guess, implements the formatting requirements of the 6th ed.)

\documentclass{article}
\begin{filecontents}[overwrite]{mybib.bib}
@article{Petkov2008,
author  = {Petkov, Christopher and Kayser, Christoph and Steudel, Thomas 
           and Whittingstall, Kevin and Augath, Mark and Logothetis, Nikos},
year    = {2008},
month   = {04},
pages   = {367--74},
title   = {A voice region in the monkey brain},
volume  = {11},
journal = {Nature Neuroscience},
doi     = {10.1038/nn2043}
}
@article{Petkov2009,
author = {Petkov, Christopher and Logothetis, Nikos and Obleser, Jonas},
year   = {2009},
month  = {07},
pages  = {419--29},
title  = {Where Are the Human Speech and Voice Regions, and 
          Do Other Animals Have Anything Like Them?},
volume = {15},
journa = {The Neuroscientist: A review journal bringing neurobiology, 
           neurology and psychiatry},
doi    = {10.1177/1073858408326430}
}
\end{filecontents}
\usepackage[style=apa,natbib]{biblatex}
\addbibresource{mybib.bib}
\usepackage{xurl}
\begin{document}
\citep{Petkov2008,Petkov2009}
\citet{Petkov2008,Petkov2009}
\printbibliography
\end{document}