Addendum to my previous comment, you can change this behavior with the -s option to `cal`:
-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.
-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.