Date conversion to specified format not working for all values

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Python

DateTime

DataFrame

I have a code that converts all the dates in the specified date column to the specified date format. In case the date is invalid or empty, it gets replaced by the replacement value specified.

My code works as expected for all values except the following two:

1. 12-2012-18 (Gets considered invalid & is being replaced by the replacement value).
2. 2008,12,02 (Converted to "02,01,2008" instead of "02,12,2008" or "12,02,2008").

What I have tried:

CODE:

def date_fun(df, col_name, date_format, replace_value):
                
            # Convert column values to string
            df[col_name] = df[col_name].astype(str)
            
            # Convert serial date values to datetime values
            def handle_serial_date(val):
                try:
                    return pd.to_datetime(float(val), unit='D')
                except:
                    return val
            df[col_name] = df[col_name].apply(handle_serial_date)
            
            # Convert regular date values to datetime values
            df[col_name] = pd.to_datetime(df[col_name], errors='coerce')
            
            # Replace invalid or null dates with the specified value (if any)
            if replace_value is not None:
                replace_value = pd.to_datetime(str(replace_value), errors='coerce') # convert replace_value to datetime format
                df[col_name] = df[col_name].fillna(replace_value) # replace invalid or null dates with replace_value
                               
            # Convert the datetime values to the specified format
            df[col_name] = df[col_name].dt.strftime(date_format)
            
            new_data = df[col_name].to_dict()
                        
            return new_data

Input & Output:

Input:
"0": 25.09.2019
"1": 9/16/2015
"2": 10.12.2017
"3": 02.12.2014
"4": 08-Mar-18
"5": 08-12-2016
"6": 26.04.2016
"7": 05-03-2016
"8": 24.12.2016
"9": 10-Aug-19
"10": abc
"11": 05-06-2015
"12": 12-2012-18
"13": 24-02-2010
"14": 2008,13,02
"15": 16-09-2015
"16": 23-01-1992, 7:45
"17": 
"18": 2nd December 2018
"19": 45678
"20": 798

Output: (format= m-d-Y, replacement value=05-06-1987 (for null & invalid dates))

            "0": "09-25-2019",
            "1": "09-16-2015",
            "2": "10-12-2017",
            "3": "02-12-2014",
            "4": "03-08-2018",
            "5": "08-12-2016",
            "6": "04-26-2016",
            "7": "05-03-2016",
            "8": "12-24-2016",
            "9": "08-10-2019",
            "10": "05-06-1987",
            "11": "05-06-2015",
            "12": "05-06-1987",
            "13": "02-24-2010",
            "14": "02-01-2008",
            "15": "09-16-2015",
            "16": "01-23-1992",
            "18": "12-02-2018",
            "19": "01-23-2095",
            "20": "03-09-1972"

The problematic rows are: 12 & 14. Why is my code not working on these two values?