How the date format works dd/mm/yyyy vs mm/dd/yyyy ?

Hello,

Our customer is confronting with a situation with the date format.

In the system the format date should be dd/mm/yyyy but I have an example of an opportunity which has 3 fields of date format type which has  two different format >> two of them have mm/dd/yyyy fromat and the 3rd one is dd/mm/yyyy.

Do you have any idea why this is happening and due to which what fact it has this behavior ?

Thanks,

Dan