8564s MARC will be synchronized after bibdocfile tables only if FFT is used or '856' tag is present in the MARC. if MARC comes with 8564s tags with bibdocfile urls (i.e. 'CFG_SITE_URL/record/123/files/docname.ext') and FFTs have not been used (e.g. because MARC is coming from bibedit/aleph/current submission), it will first import $y and $z (description and comment) from MARC into bibdocfile, and then rebuild all 8564s based on bibdocfile.