LEED Addenda are issued regularly to update USGBC's LEED rating systems and reference guides with any changes or improvements. They clarify, correct, interpret or provide alternative language to the current rating system guidance.
You can search for Addenda in the Addenda Database. They also are published in tables, organized by page number of the LEED Reference Guides, such as this one for LEED for Neighborhood Development. These tables are published in the USGBC Resource Library.
Take a look at our Help Center LEED Addenda section for more answers to specific Addenda questions.