The -l flag added for http://rhn.redhat.com/errata/RHBA-2005-309.html (bug #146214) is not documented in the man page, or mentioned in the -h output.
$ man useradd ... -l Do not add the user to the last login log file. This is an option added by Red Hat. ... $ rpm -q shadow-utils shadow-utils-4.0.3-60.RHEL4