If you only have a day and month like 25th December you should represent it with a type that contains just that information. Java for example has the MonthDay c

If you only have a day and month like 25th December you should represent it with a type that contains just that information. Java for example has the MonthDay class (https://docs.oracle.com/javase/8/docs/api/java/time/MonthDay.html https://docs.oracle.com/javase/8/docs/api/java/time/MonthDay...) which can be converted into a local date when the additional information is available. If your users want to refer to that as a date then that should be handled in the UI but should not lead to ambiguity in the internal representation.