I read two papers just published online (paper no.1 accepted about 1 month before paper no.2) in the same journal by the same authors. Two papers have the same topic, using the same numerical method, same at least one simulation object. I found in paper no.2 some figures that very similar to paper no.1. The example of the figure in these papers shows in the picture below. Fig C is exactly the same in the two journals (just change the view angle a bit) while Fig A, B, C, and D are different. However, there is no statement that the data in Fig C has been published in paper no.1 and no citation. Additionally, there are also some similar figure data in the two papers but just change the axis scale. So can it consider as duplicate data?
Duplicate data is mostly a problem when the data are experimental/real-world data and where repeating an analysis with the same data makes the overall literature seem to support a conclusion more strongly than it would if it were presented only once.
Let's say you have an experiment showing that green jelly beans cause acne. You publish it once, but people keep some healthy skepticism. Now suddenly 2 more papers appear that say green jelly beans cause acne... oh my! This is becoming quite the interesting field of study! Well, if these are 3 independent data sets, it appears to be a fairly strong conclusion supported by replication. If they're actually the same data set analyzed 3 times, now the authors of the second two papers have committed academic misconduct if they haven't made it clear that this is the same data. If you were conducting a meta analysis you would want to be careful not to include more than one of the studies.
The second issue is with copyright of figures. Typically the journal publishing a paper has copyright of figures published in that journal. Copying a figure from one paper and presenting it in another may violate that copyright. However, you can't copyright data itself, and there are only so many ways to plot some types of data, so the extent to which this sort of copyright is valid is quite narrow.
In the situation you describe, you have simulated data. The jelly bean issue isn't really relevant for simulated data. The papers are also in the same journal, so it's not going to argue with itself that the figures are too similar to a copyrighted figure that they own the rights to (to cover all the bases they could ask themselves for permission, but why?).
If the simulated data are created by some complex methodology, it is important to cite a previous paper using the same methodology to properly credit those authors, but sometimes this isn't really necessary. For example, if I generate simulated data by adding noise to a sine wave, it's probably sufficient to describe this. Sure, if another paper in a very similar area used exactly the same parameters, it's good to cite it to be thorough, but a sine wave plus noise isn't really much of an intellectual contribution and if it's skipped I don't think any major crime is committed. Maybe less so if it's the same authors not self-citing.
The only issue I can possibly see here is that the authors have perhaps padded their publications a bit by splitting one paper into two and publishing them separately. Reviewers can certainly comment on this, and can argue that the similarity of the second paper to the first makes it less suitable for publication, but this has very little to do with one set of simulated data that are the same/similar in the two, it has more to do with the rest of the publication.
I'm not sure why you're worried about this case except for some perceived unfairness in how you were treated versus them, but I don't see any benefit to you in pursuing this any further.