Should a PhD thesis reflect the state of research at the time of writing? I am currently writing up my PhD thesis and have the following issue. I wrote a paper during the PhD thesis, the result of which was developed further by third parties without my involvement. From the perspective of my published paper, this new result lies in the future and is of course not mentioned in the paper. However, at the time of writing the PhD thesis, this result is available and may be relevant for the readers of the PhD thesis.
Should the PhD thesis contain a reference to the third party paper?
Presumably the answer to above question is yes in one form or another. A more detailed question is then: How should it be included? I can imagine multiple options.

If the result is relevant to the general scientific scope of the thesis it probably warrants an explicit mention in the introduction, explaining that the work is based on the result in the thesis.
Let's say there is a close technical connection and the third party paper improves upon some aspects of the original result. Would it be appropriate to even summarize this progress rather than simply mentioning it?
If the result is not directly relevant to the scientific scope, it is presumably omitted in the thesis.

This question is generally about whether the PhD thesis is meant to reflect the state of research at the time of writing or at the time of the published results that are summarized in the thesis. An answer to the above examples would already give a lot of insight, but I am also interested in the general attitude towards this issue.
As a side note: In some countries, cumulative theses (also called &quot;staple theses&quot;) are allowed, which are simply an accumulation of the published papers with an introduction added. Since this form would most likely not contain any mention of the third party paper, I started thinking about what a normal PhD thesis should be doing in this regard.
Some options:

Explanatory footnotes often work well and can be used to 'talk across time' so to speak;
Appendices can also be used for covering material that may be out of sink, if you think you need to go into more detail;
An afterword can also be an appropriate way of accounting for developments between the time of writing and the time of publication. This is fairly common practice.

Basically most examiners will view the dissertation as YOUR journey through the research, rather than as an exact snapshot of the state of play in your area.
HOWEVER - they will be looking for (and be impressed by) you demonstrating that you know what good practice looks like in your field of research, and this extends to how you handle (and acknowledge) circumstances of this kind.