I am reviewing a research paper. In the reference section of the paper, the authors have mentioned two previous works that are based on the same topic:
- Author X, Author Y, Author Z, "Topic_Name" appeared at ABC conference 2020.
- Author P, Author Q, Author R, "Topic_Name" appeared at MNO conference 2020.
In the introduction section, the authors used the following sentence:
"Author X and Author P [1,2] began the study of the Topic_Name."
They did not use "et al." when using this statement. Is this allowed? since it looks as if Author X and Author P are the only authors and they worked in collaboration to study the topic.