> Consider "200". Is this the year 200? Is this the 200th day of the current year? Surprise, in ISO 8601 it’s neither — it’s a decade, spanning from the year 2000 to the year 2010. And "20" is the century from the year 2000 to the year 2100.

In any sane system, giving a function "200" as an input and asking what date/datetime it represents should return some sort of error.

Some inputs are too ambiguous to meaningfully parse.