This is a pretty good public article on the topic of copyright notices in open source projects: https://www.linuxfoundation.org/blog/blog/copyright-notices-in-o

This is a pretty good public article on the topic of copyright notices in open source projects: https://www.linuxfoundation.org/blog/blog/copyright-notices-in-open-source-software-projects https://www.linuxfoundation.org/blog/blog/copyright-notices-... although it doesn't explicitly address why the date can/should be omitted. The way I would put it: copyright notices in open source projects are typically not intended to function as formally (under US law) correct copyright notices, which do require a year. Rather, they serve different purposes for which the year is not necessary. And if you do include a year, the notice is likely to become inaccurate over time, which will make it formally invalid (under US law). That is not likely to be significant, but it makes inclusion of the year relatively pointless, in relation to the labor that would be involved in attempting to keep the year accurate.