VMS Help LBR Routines, LBR$DELETE_DATA, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    If you want to delete a library module, you must first call
    LBR$DELETE_KEY to delete any keys that point to it. If no library
    index keys are pointing to the module header, LBR$DELETE_DATA
    deletes the module header and associated data records; otherwise,
    this routine returns the error LBR$_STILLKEYS.

    Note that other LBR routines may reuse data blocks that contain
    no data.