Im in the Applied Computer Science field (deploying technologies in different areas of society). I published a conference paper last year on one such case study and wanted to reuse this data to create a longer, journal paper about the socio-political realities and broader societal reflections on this work (which was not appropriate for the conference audience).
Im wary of self-plagiarism, so the question is: is it possible to take this same idea and publish it in the journal, if the quotes and participant comments are carried across, does it invalidate my claim to this being unpublished work? (Both SAGE Journals and Elsevier have a journal submission policy that only unpublished writing such as thesis, conference posters etc. can be used for journal writing: Prior Publication: SAGE Journals
If a substantial portion of your manuscript has been previously published, your manuscript will generally not be acceptable for publication in a SAGE journal. However, subject to each journal’s policy, there are certain circumstances where material that has been publicly distributed may be considered for publication.
Does rewriting relevant sections that I will be re-using from the conference publication count as a portion from previously published piece?
Similar answers from Academia SO cover some elements of this question, but my question is about the Findings (Participant Interview quotes) being carried over and the other aspects being fresh.
Any help with this, or links to resources that help appreciated!