> This leaves ambiguous how to refer to decades like 1800-1809. There is the apostrophe convention for decades. You can refer to the decade of 1800–1809 as "th

> This leaves ambiguous how to refer to decades like 1800-1809. There is the apostrophe convention for decades. You can refer to the decade of 1800–1809 as "the '00s" when the century is clear from the context. (The Chicago Manual of Style allows it: https://english.stackexchange.com/a/299512 https://english.stackexchange.com/a/299512.) If you wanted to upset people, you could try adding the century back: "the 18'00s". :-) There is also the convention of replacing parts of a date with "X" characters or an em dash ("—") or an ellipses ("...") in fiction, like "in the year 180X". It is less neat but unambiguous about the range when it's one "X" for a digit. (https://tvtropes.org/pmwiki/pmwiki.php/Main/YearX https://tvtropes.org/pmwiki/pmwiki.php/Main/YearX has an interesting collection of examples. A few give you the century, decade, and year and omit the millennium.) Edit: It turns out the Library of Congress has adopted a date format based on ISO 8601 with "X" characters for unspecified digits: https://www.loc.gov/standards/datetime/ https://www.loc.gov/standards/datetime/.