Currently, there aren't many "sub-tags" in the bibliographies tag area -- there's citing and sorting, and there are the "package" tags like biblatex and natbib (which nowadays are used without adding bibliographies).
From my experience, there are more and more questions about multiple and/or subdivided bibliographies, and these questions are hard to find among the many hundred bibliography questions (which contributes to new duplicate questions). Therefore, I suggest to create a bib-segmenting tag and to add it to the appropriate questions (slowly and starting with the highest-scoring ones). As an alternative, one could choose a general name (segmenting) for the new tag so that it could be used for the (few) questions about multiple/subdivided indexes and glossaries as well.
Note: I wouldn't use sectioning to mark the questions at hand because this tag is traditionally about tinkering with
\section & friends, which requires a different kind of expertise.
EDIT: Inspired by barbara beeton's comments, I'm leaning towards a general tag called subdividing.