my birthday is at the end of the month, during a processing of a document for my US visa 10+ years ago, I was dealing with 2 different sites, one accomodating my local date formatting, and one fixed for the US standard. I was puzzled that I had been made 2 years younger when verifying my data, turned out my birth date of month was now month number 24+ of the year, pushing my birth ahead, and my birtb month had become my birth date of month.