It seems the texinfo documentation and the documentation on the web site
would need an update, too. The web site docs start with "last updated
March 16, 2018" and the manual starts with "GNU Datamash (version 1.3,
25 January 2018)."
https://www.gnu.org/software/datamash/manual/
https://www.gnu.org/software/datamash/manual/datamash.html
The current texinfo documentation does not mention -C, --skip-comments.
https://git.savannah.gnu.org/gitweb/?p=datamash.git;a=blob;f=doc/datamash.texi;h=3bce3f4fced2601f08d86a16c527e0f0a5d996cf;hb=HEAD