Meaning of et al. when referring to multiple papers with the same first author

I understand this "X and others" to mean one specific set of (unnamed) people, unless they are the same bunch I'd write them separately. Just like when I was citing two papers by Chen together, but they were different Chens. Perhaps use "X, Y et al. [203] and X, Z et al. [205]"?

In my experience with engineering, I usually see X and coworkers [1,2] in these situations. I have no knowledge if it is grammatically incorrect to use et alia ("and others") to refer to multiple papers with different authors, but I haven't ever noticed it being used that way. Also, you may come across the convention that it is not necessarily the first author used with X and coworkers, for instance, if the works all come from the lab of a well known researcher, one might prefer Smith and coworkers [1-3], where Smith is the PI of the lab.

See also this answer from Strongbad to a related question.

Remember that no matter what you write in the text, the really important thing is the bibliographic item. I would personally tend to avoid using X et al. [1,2] if [1] and [2] do not have the same list of authors. If I came to this point in writing, I would try to reword the sentence.

On the other hand, I would use sensible judgement. If it's clear that the articles come from the same group of investigators, just with one name missing or so, you are probably fine keeping the two things together.

Some other "out-of-the-box" options include:

• Using [XYZ12] citation style; then it's clear that X et al. [XYZ12, XAB13] do not have the same list of authors.

• Avoid putting people's names in front of the citations (not preferable in general I think)

• Use more than one name before et al.