Fix Czech Rodné číslo check digit validation

It seems that a small minority of numbers assigned with a checksum of 10
are still valid and expected to have a check digit value of 0. According
to https://www.domzo13.cz/sw/evok/help/born_numbers.html this practice
even happended (but less frequently) after 1985.

Closes #468

Author: arthurdejong

stdnum/cz/rc.py

@@ -1,7 +1,7 @@
 # rc.py - functions for handling Czech birth numbers
 # coding: utf-8
 #
-# Copyright (C) 2012-2019 Arthur de Jong
+# Copyright (C) 2012-2025 Arthur de Jong
 #
 # This library is free software; you can redistribute it and/or
 # modify it under the terms of the GNU Lesser General Public
@@ -90,14 +90,10 @@ def validate(number):
     if len(number) not in (9, 10):
         raise InvalidLength()
     # check if birth date is valid
-    birth_date = get_birth_date(number)
-    # TODO: check that the birth date is not in the future
+    get_birth_date(number)
     # check the check digit (10 digit numbers only)
     if len(number) == 10:
-        check = int(number[:-1]) % 11
-        # before 1985 the checksum could be 0 or 10
-        if birth_date < datetime.date(1985, 1, 1):
-            check = check % 10
+        check = int(number[:-1]) % 11 % 10
         if number[-1] != str(check):
             raise InvalidChecksum()
     return number

tests/test_cz_rc.doctest

@@ -0,0 +1,36 @@
+test_cz_rc.doctest - more detailed doctests for stdnum.cz.rc
+
+Copyright (C) 2025 Arthur de Jong
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public
+License as published by the Free Software Foundation; either
+version 2.1 of the License, or (at your option) any later version.
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with this library; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA
+
+
+This file contains more detailed doctests for the stdnum.cz.rc
+module.
+
+>>> from stdnum.cz import rc
+
+
+
+These have been found online and should all be valid numbers.
+
+>>> numbers = '''
+...
+... 8801251680
+...
+... '''
+>>> [x for x in numbers.splitlines() if x and not rc.is_valid(x)]
+[]