Somewhere in the code is also/still a seperate check concerning strftime:

PythonWin 3.2 (r32:88445, Feb 20 2011, 21:29:02) [MSC v.1500 32 bit (Intel)] on win32.
Portions Copyright 1994-2008 Mark Hammond - see 'Help/About PythonWin' for further copyright information.
>>> import datetime
>>> datetime.datetime(-1, 1, 1)
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
ValueError: year is out of range
>>> datetime.datetime(0, 1, 1)
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
ValueError: year is out of range
>>> datetime.datetime(1, 1, 1)
datetime.datetime(1, 1, 1, 0, 0)
>>> datetime.datetime(1, 1, 1).strftime("Y")
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
ValueError: year=1 is before 1000; the datetime strftime() methods require year >= 1000
>>>