As you may know, the Library of Congress actively maintains its subject headings. Not surprising to anyone other than purveyors of fixed ontologies. New subjects appear, terminology changes, old subjects have new names, etc.
The Subject Authority Cooperative Program (SACO) has a mailing list:
About the SACO Listserv (sacolist@loc.gov)
The SACO Program welcomes all interested parties to subscribe to the SACO listserv. This listserv was established first and foremost to facilitate communication with SACO contributors throughout the world. The Summaries of the Weekly Subject Editorial Review Meeting are posted to enable SACO contributors to keep abreast of changes and know if proposed headings have been approved or not. The listserv may also be used as a vehicle to foster discussions on the construction, use, and application of subject headings. Questions posted may be answered by any list member and not necessarily by staff in the Cooperative Programs Section (Coop) or PSD. Furthermore, participants are encouraged to provide comments, share examples, experiences, etc.
On the list this week was the question:
Does anyone know how these three sites differ as sources for consulting approved subject lists?
http://www.loc.gov/aba/cataloging/subject/weeklylists/
Janis L. Young, Policy and Standards Division, Library of Congress replied:
Just to clarify: all of the links that you and Paul listed take you to the same Approved Lists. We provide multiple access points to the information in order to accommodate users who approach our web site in different ways.
Depending upon your goals, the Approved Lists could be treated as a subject that has three locators.