The Decade Still Has a Year Left
Friends! Netizens! Countrymen! The Dionysian era and the Common Era have no year 0 (because 0 did not exist in Europe when the Venerable Bede popularized numbering years by “the year of our lord”) so in those systems a decade runs from year 1 to year 10 and a century runs from year 1 to year 100. The 20th century runs from 1 January 1901 to 31 December 2000, and the 2010s run from 1 January 2011 to 31 December.
Unless you are an astronomer working in Julian days with a year 0 (= 1 BCE in the Common Era) the decade still has a year and a day left. If it were the other way round, then the first decade would only have 9 years (1 CE to 9 CE) and the first century would only have 99 years (1 CE to 99 CE) and all the others would have 10 or 100.
{this is a message from your local tablet scribe- if its really important, ask an expert in the scribal art}
{computer scientists- warning you against off-by-one errors since ENIAC}
I covered the only century years divisible by 400 are Leap Years topic back in Astro 2000, but had to bring in my textbook to convince my systems analyst to let me code our Date binary to packed and text subroutine to allow for that.
There was a recent example of a year 2020 problem in the Hamburg transit system.
https://www.abendblatt.de/hamburg/article228038743/U-Bahn-Hamburg-DT5-ausgefallen-Hochbahn-Software-Fehler-Verkehr-Verspaetung-Stoerung.html
Did Cuneiform scribes ever shorten dates to save space on clay tablets?
I guess people have forgotten from 2000 and 2010.
Someone re-posted the old joke about the software engineer who dies of a heart attack in 1999 due to Year 2000 stress and has their body frozen. They are woken up in the year 9998 because humans have solved hunger, war, and ecological troubles but they just finished a code review of the interstellar banking system and their experts need some help with a language called Cobol.
Everyday dated documents are not good at distinguishing between kings with the same name like astronomical texts are, so if you have a text from the 2nd year of Darius or Artaxerxes it can be hard to know which Darius or Artaxerxes. And Assyrian texts are often missing the date entirely and just addressed to “the king.”