What subsystem was this in?
Most software project don't make a definitive list of their subsystems, so the subsystems tags are our curators' best guess at what part(s) of the system a vulnerability was in. Often, curators will look at file paths primarily, but may also look at bug reports or commit messages to make this determination.
As part of the editorial process, we periodically combine subsystems together. If you see two subsystems that ought to be combined, then do a pull request against the vulnerabilities involved! We welcome that kind of edit.