For anyone interested in such oddities, here's an email from a DEC engineer in response to an alleged bug report back in the 90s that goes into a brief but very deep dive of the history of calendar, including the jewel about the jump between the Julian and Gregorian calendars (and the continuity of the days of the week):
More to the point, that email suggests that there's a good chance the continuity of the days of the week predates even the Gregorian calendar and goes back to the founding of the Roman empire, as presumably Mercedonius wouldn't have given anyone a reason to suddenly change the days of the week.
Does my unix date utility take into account these occasional leap seconds? And are these just hardcoded in the library itself and updated once in a while?
...which can be added to ntpd's configuration if you want your system's leap second to occur exactly on time.
Even if you don't, the leap second will eventually take effect via an update from your configured remote ntp servers, or your GPS source, or wherever you get your time from.
https://neosmart.net/forums/threads/an-extended-history-of-t...
More to the point, that email suggests that there's a good chance the continuity of the days of the week predates even the Gregorian calendar and goes back to the founding of the Roman empire, as presumably Mercedonius wouldn't have given anyone a reason to suddenly change the days of the week.