A project I am following uses the WTFPL but updated the text to replace the copyright statement
Copyright (C) 2004 Sam Hocevar <email@example.com>
with the project author's name and email address, and the year that they adopted the license.
I tried to convince them that the copyright statement pertains to the license itself, and that they should not change it; but I find it hard to find any resources to support my understanding.
Are there web pages or other public and ideally reasonably authoritative documents or statements which clarify this? Or could you argue that my interpretation is correct or incorrect based on general principles?