I think the world could use an “imprecise” data type, which would be a tuple (t, margin).

In your case: if you wanted a date plus minus 50yrs, that would be (date(d), range(years, 50)).

Some construction like this allows for I believe most use cases. You just need to be able to store: date, date time, date range, and the precise/imprecise versions of all of these.