Dates That Don't Exist (2015) | Hacker News

A Hacker News thread discussed an article about dates that effectively did not exist because of calendar reform.

Commenters debated the proleptic Gregorian calendar, country-by-country adoption dates, and how historical dates should be interpreted.

They also compared how tools like Perl DateTime, OpenBSD cal, and Ubuntu ncal handle calendar switches.

The takeaway is that calendar history differs by country, so naive software date conversion can produce misleading or impossible results.