My instance of cal (MacOS 14.5) has this in the man page:

     -s country_code

             Assume the switch from Julian to Gregorian Calendar at the date

             associated with the country_code.  If not specified, ncal tries

             to guess the switch date from the local environment or falls back

             to September 2, 1752.  This was when Great Britain and her

             colonies switched to the Gregorian Calendar.


Note that the switch to the Gregorian calendar happened at different times in different countries.  In Catholic-dominated countries it happened in October of 1582.  The English-speaking world, being Protestant-dominated, waited until September of 1752 to adopt it.
=====
nygeek.net
mindthegapdialogs.com/home


On Wed, Jul 10, 2024 at 9:25 PM Dave Horsfall <dave@horsfall.org> wrote:
The manpage for "cal" used to have the comment "Try September 1752" (and
yes, I know why); it's no longer there, so when did it disappear?  The
SysV fun police?

I remember it in Ed5 and Ed6, but can't remember when I last saw it.

Thanks.

-- Dave