Date format issues

Hi I am having problems with one column of dates whereby some are in date format and others visually appear to be but are not. I know they are not as when I create a separate column and try to extract the =YEAR(A1), only those cells which are in fact date format show the correct result. If I format the column of dates as a date, and then try to extract the year, I still get multiple failures returning "VALUE". I have noticed that the values that fail are ones with single digit months i.e. 6-06-2020 instead of 06-06-2020.

The file is extracted from a database which has thousands of lines and is formatted as an excel table, I have attached a small sample group in this file.

Any help would be greatly appreciated.
Thanks