File Tags (also known as Stub Files or Purged Files) on the Extended Drive have a reference to the media that the files are written to with DX. The reference to the media is contained within the Master File Table (MFT.) The MFT contains the MediaID that is stored in the registry and does not reference the media by it's media name. If the MediaID changes for any reason, the File Tag in the MFT will not point to the correct media by it's MediaID, the the File Tag is considered to be an Orphaned File Tag.

Purged files remain accessible through file tags on the extended
drive. When a file has been migrated to a single piece of media, a file tag
consumes between 0 bytes and 1 cluster of disk space. (On Microsoft Windows
NTFS systems, a cluster of disk space averages approximately 4 KB, although the
size depends on a number of variables.)

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