The Library of Congress has finally decided to separate the genre form terms from the subject headings. Since 2007 the Library of Congress’ Policy and Standards Division has been developing genre/form terms, and in June 2010 determined that the new thesaurus, Library of Congress Genre/Form Terms for Library and Archival Materials (LCGFT), should be formally separated from Library of Congress Subject Headings (LCSH).
As of May 24, 2011, new coding should be used when assigning LCGFT terms in bibliographic records. That coding is as follows.
655 #7 $a [Term]. $2 lcgft (Library of Congress genre form term)
We will no longer use $2lcsh (Library of Congress subject heading)
CAUTION : The change in coding applies only to headings that have an LCGFT authority record (tag 155), and not to headings that are being used in a 655 field but are from LCSH (tagged 150). Therefore, the headings would look like this:
655 #7 $a Horror films. $2 lcgft (there is a 155 authority record) OR
655 #7 $a Political fiction. $2 lcsh] (there is not a 155 authority record, but there is a 150 tag.
For further information and the rationale for these revisions, please see the January 3, 2011 announcement, “Library of Congress to Reissue Genre/Form Authority Records.” http://www.loc.gov/catdir/cpso/gf_lccn.html
A related document from OLAC (OnLine Audiovisual Catalogers electronic discussion list)