Q: Can I use the data of Part C to expand the published article?

You are right, using data from one part of the original study for a new article with a more detailed analysis and additional content will not amount to a duplicate publication. However, segmenting results from the same data set into different manuscripts might be considered “salami slicing.” If the new paper tests a different hypothesis as opposed to the 2019 study or has a distinct methodology (in your case, perhaps additional experiments and content), then it is acceptable to publish it separately, and it will not be considered salami slicing either. It is imperative, however, that you cite the 2019 paper in the new paper.

You may have a look at similar questions we have answered for some researchers:

• If the dataset and method for two papers are the same but the result is different, would they be considered a case of salami slicing?
• If I develop and submit two papers for (from) a questionnaire survey, would it be considered salami slicing?

Hope this helps. All the best for your study!