As you mentioned, FSF and CC recommend the following blurb for CC0 licensed files:
https://wiki.creativecommons.org/wiki/CC0_FAQ#May_I_apply_CC0_to_computer_software.3F_If_so.2C_is_there_a_recommended_implementation.3F
So I fail to see what is unclear for projects that wish to use CC0.
In the GNU project we don't use CC0, so our requirements are tailored
for the licenses that we do use.
