Peer review: Is this "citation tower" a bad practice? I am peer-reviewing an article &quot;A&quot; and I found something interesting. The authors use a mathematical lemma (which is just an inequality) for which they cite article &quot;B&quot;. I have used this inequality before for many years, but noticed that &quot;B&quot; is an article from 2019, so evidently this inequality wasn't discovered/derived for the first time in &quot;B&quot;.  I was curious so I managed to obtain this article &quot;B&quot; and noticed that they use the same inequality by citing article &quot;C&quot;. A similar thing happens in &quot;C&quot; by citing &quot;D&quot;, and so on until we get to &quot;F&quot;. Notice that in this whole &quot;citation tower&quot; no new information is added: the mathematical lemma remained essentially the same.
Moreover, some of the same authors appear in some of the works A,B,...,F but not in all and not consecutively. However, an author of &quot;A&quot; is also an author of &quot;F&quot;. Finally, in &quot;F&quot; (which is an article from 2011) the authors provide the mathematical lemma, and provide a proof for it. However, I have seen other works in the literature which uses this result even before 2011, and actually I can track it all the way until I reach a famous (but OLD) book &quot;Z&quot; which provides the same inequality but not necessarily using the same notation.
Do you think this &quot;citation tower&quot; (is there another name for this practice?) is a bad enough practice to point it out in my review? Up to now I am considering the following things to do with my review (regarding this issue only):

Do nothing. The authors are using a result from the literature by appropriately citing it.

Just suggest them to cite &quot;F&quot; instead of &quot;B&quot;.

Suggest them to cite &quot;Z&quot; instead of &quot;B&quot;.


However, since an author of &quot;A&quot; is also an author of &quot;F&quot;, under the assumption that this citation tower is indeed a bad practice, and that the result was given in &quot;F&quot; as if it was discovered there even when this result was known many years before, there is a fourth option:

Point them out this issue describing it as a bad practice in order to help preventing it in the future. Moreover, I was thinking in asking the reviewers to cite &quot;F&quot; and adding a note in the final manuscript saying that the result was shown in &quot;F&quot; using modern notation, but it was known to be true since &quot;Z&quot;.

EDIT AFTER SUBMITTING MY REVIEW: It is very hard to chose a correct answer, since I don't believe there is a single one. There are very nice answers here, but I will mark as correct the one that mostly resembles what I did at the end.
I think this requires some nuance. You seem to suggest that citing the earliest usage is preferable, and it might be. But it might also be the case that each subsequent usage adds something to the context. That is to say that the citation appears in the chain for some particular use and the reader of the current paper might find it useful to explore that history. Each of those citations is surrounded by context that can be useful.
If you always cite only the earliest usage, then the reader has no hints about the overall usage context of that thing cited. And the current author might be inviting the exploration.
Of course, it might also be that the author(s) considers the lemma to be a minor point and has used the citation they found without chasing the chain back themself, not seeing any need for it in the current context.
Overdone, in mathematics, we just always cite Euclid.
So, I don't think citing a later, rather than an earlier paper is a bad practice necessarily, but could be in a particular instance.
You can always note the other citations in your review and point to the earliest one without making any specific recommendation.