Date Format Changing Program Not Working

[pyth0nus3r]

So below is the program that I am using to change files with European (DD-MM-YYYY) style date to American (MM-DD-YYYY) Style Date:

#! python3
   # renameDates.py - Renames filenames with American MM-DD-YYYY date format
   # to European DD-MM-YYYY.

import shutil, os, re

# Create a regex that matches files with the American date format.
datePattern = re.compile(r"""^(.*?) # all text before the date
    ((0|1)?\d)-                     # one or two digits for the month
    ((0|1|2|3)?\d)-                 # one or two digits for the day
    ((19|20)\d\d)                   # four digits for the year
    (.*?)$                          # all text after the date
    """, re.VERBOSE)

# Loop over the files in the working directory.
for amerFilename in os.listdir('.'):
    mo = datePattern.search(amerFilename)

    # Skip files without a date.
    if mo == None:
        continue

    # Get the different parts of the filename.
    beforePart = mo.group(1)
    monthPart  = mo.group(2)
    dayPart    = mo.group(4)
    yearPart   = mo.group(6)
    afterPart  = mo.group(8)
    
    # Form the European-style filename.
    euroFilename = beforePart + dayPart + '-' + monthPart + '-' + yearPart + afterPart
    
    # Get the full, absolute file paths.
    absWorkingDir = os.path.abspath('.')
    amerFilename = os.path.join(absWorkingDir, amerFilename)
    euroFilename = os.path.join(absWorkingDir, euroFilename)
    
    # Rename the files.
    print('Renaming "%s" to "%s"...' % (amerFilename, euroFilename))
    shutil.move(amerFilename, euroFilename) 

However, the files whose days that have 20-29 in their dates does not work properly.
For example, ab12-10-2010test.txt works but ab22-10-2010test.txt does not work.
Is there some problem with the regular expression.