Do you have a source for that?
EDIT: #19 here https://www.ibiblio.org/harris/500milemail-faq.html
EDIT: #19 here https://www.ibiblio.org/harris/500milemail-faq.html
It's also entirely plausible that a local definitions file was used to provide the unit that didn't come in the default install. Hence the anachronism is merely "potential" instead of "definite"