I have been known to put in a false date of birth when creating a website account. Sometimes there’s no good reason why a particular organisation should have this piece of key information.
So when my DOB was rejected when trying to log into an old, redundant Apple account (so I could remove it), I wasn’t too surprised.
But after several abortive attempts at alternative solutions to the problem I discovered that my DOB was acceptable if I entered the day as the month and the month as the day. ie My DOB had been recorded as the 4th November rather than the 11th April.
I guess it’s an American v British date thingy.