I've found a bug in Debian Linux 10 (buster) CLI cal application. If you call call 1752 you will see in the output the month of September is not complete, missing days 3-13. I tryed it in Python 3 (through BPython 3), using calendar module:
import calendar as c
c.prcal(1752)
and all months of 1752 show correct). The bug seems to be present only in the CLI cal Linux application.
As a consequence of this little bug, ALL YEARS previous to 1752 are output incorrectly from cal CLI.
Does anybody know anything about this bug?
September 1752 had fewer days in Great Britain and their colonies at the time (i.e. also what became the United States) because that's when they switched to the Gregorian calendar. See e.g. https://www.timeanddate.com/calendar/julian-gregorian-switch.html
This isn't a bug.
The behavior will obviously also depend on your locale.