Where is it acceptable to mention an abnormally high stipend? Student X's GRA stipend is more than double that of their peers in the same major. They wonder if this is appropriate to mention this as a negotiating tool in certian scenarios. One reason for this is their past merit and performance. Another major reason is that they are in an interdisciplinary field, and their expertise leans towards the more higher paying portion of that interdisciplinary field.
I will start with the scenarios where I think it is likely most appropriate – and go from there.
Salary Negotiation:
Should they mention that their stipend was higher than peers in the same field, thus they should have a higher staring salary than their peers? Would this matter more or less for a fellowship?
Interviews:
Should this be mentioned during an interview before salary negotiations to attest to ones merit and domain expertise?
PhD Applications:
Probability would sound bad to mention here. How would you feel if an applicant mentioned that they were awarded a stipend at double the rate of their peers?
Resume:
Similar to reasoning stated in 'PhD Applications'.
Grants &amp; Scholarships:
I think this could be a negative to mention here. Obvious reasons. That is why I put it last.

One might say, &quot;Why not focus on the reasons why their stipend is
higher in terms of merit and domain expertise for all of the above?&quot;
The reason one may want to use explicitly state that they were awarded
more is as a proof of merit and domain expertise.
Salary negotiations are about supply and demand.  If your stipend has come to an end, it is no longer relevant to that supply and demand.  If your stipend is ongoing, you can say you will only accept a new position if it pays more than the stipend.
Your past stipend pay is not very convincing evidence of your merit.
Your past stipend pay is not relevant to the selection of PhD students.  Discussing money may give the impression you would be more suited for an industrial position.