Arr[0] is the first element of an array, not the “zeroth”.
There is no year zero. Trying to compute with one is almost certainly an error. Trying to work with it is like dividing by zero - it does not make sense.
The year "1" was originally a Julian Date. Using a Gregorian Date before the calendar was introduced is almost certainly an error.
For ancient things, use Before Present, where I believe Present is defined to be sometime in 1950 or there about. For "modern" things (varying definitions of modern) use a sensible format/calendar that works in your database.
It's just an extrapolation; using the calendar being used at the considered time would be meaningless for us, e.g. the short-lived french republican calendar [1].
[1] https://en.wikipedia.org/wiki/French_Republican_calendar