When use `coerce=True` in `pandas.to_datetime` old dates (before 1677-09-22) return NaT. The same dates without `coerce` are parsed correctly: ``` print pd.to_datetime('13000101', format='%Y%m%d', coerce=True) print pd.to_datetime('13000101', format='%Y%m%d') ``` returns ``` NaT 1300-01-01 00:00:00 ``` pandas: 0.15.2 numpy: 1.9.1