SQL & PL/SQL

hi, I am getting daily basis data from third party in excel format which i am converting into CSV format and then uploading into oracle tables using External tables.Now problem is that every time i getting the dates in diff format i.e. sometimes dd-mon-yyyy , dd/mm/yyyy etc.

Now every time i have to open my code and change it there ...to make it as oracle date format.

IS there way i can find out format of date and based on format i can do operations with getting errors every time.

Kindly note that i m storing the TP(Excel date) date into varchar columns only and then varchar2 column value i m inserting/updating into date format using to_Date ().

Thanks