Tables of contents are as much core metadata as any of the "controlled vocabulary" data, since they provide so much free-text subject fodder for patron searches in our catalogs.  This explains why we often cache this data to enable search against it in spite of its non-presence in our physical record structure.  One might also argue that linked NAF (but not SAF, which only appears in its controlled state) data could be subsidiary, since these are primarily controlled vocabulary for personal, corporate or meeting names already on board in other parts of bibliographic description, such as in author or publisher statements and notes.  Useful for collocation yes, and perhaps for strictly "author" searches, but not required for presentation.  OCLC has certainly argued in the past that descriptive metadata is not necessarily "ours" and indeed linked data has the potential to make it possible to simply haul descriptive metadata out of WorldCat for display in our local catalog, if we haven't already given over to the utility for direct provision of our catalog (e.g., WCL).  This would solve the problem of maintaining serial records through their life cycle, assuming that CONSER and/or utility members are maintaining serial records in the utility better than we are within our local catalogs.  We need to widen our consideration of linked data to encompass descriptive metadata as well.