They can be inconsistent w.r.t is January the zeroeth month or the first month. Is Sunday the zeroeth day of the week or the first day or is ti even Monday. We have to origins for the zeroeth second a Unix version and a NTP version. Then there added variations in conversion to local time wrt how DST is encoded.
I'd vote for NTP time and January being the first month and Sunday the first day since 0 for dates is never used except by coders to make array referencing easier. All libraries should support local time most of us aren't doing astronomy and need UTC or sidereal time or mean solar time.