Is this new? I can't find previous version of this page on Internet archive and the page footer did not get updated since 2013 (at least it suggests that the content updated last time in 2013)
The "2013" is the copyright date of the initial publication of the online edition of The Feynman Lectures on Physics, but that edition (as well as the printed edition) and the Feynman Lectures Website where it is published is far from static. I have been working on it continuously since 2006 (with occasional help from volunteers), during which time a lot of improvements have been made and much new material has been added (to the website - we are not adding new material to the printed edition, though we have made, and continue to make, corrections, as needed).
> Copyright © 1963-1965, 2006, 2013 by the California Institute of Technology, Michael A. Gottlieb and Rudolf Pfeiffer
Edit: It seems that I'm wrong. There is mention that they updated Original Course Handouts in 2022
> 6. Updated in March 2022 with a new presentation featuring deep-zoomable images.