The Library of Congress Classification (LCC) system is revised and updated periodically to keep up with changes in knowledge and technology. The frequency of updates to the LCC system can vary, as the revision process is a significant undertaking that requires a lot of time and resources. In the past, the LCC system has been revised approximately every 20-30 years, although this can vary depending on the specific needs of the system and the resources available for the revision process. The most recent major revision of the LCC system was completed in the late 1990s, and a new revision is currently in progress. It is not uncommon for smaller updates and changes to be made to the LCC system on a more frequent basis between major revisions.