MC is working correctly.
The [Date] field in MC isn't just the month and day. It is a fully qualified Year, Month, Day, Time value, such as "13/03/2020 7:11 pm" which is stored in MC's Library field as a numeric value using standard practice. In this case, the stored value is "43903.799317129625706", where "43903" is a specific day, and ".799317129625706" is the time of day. Have a look at the raw data in the [Date] field by creating an expression column in an appropriate View, and entering the expression [Date, 0]. The column will then show the numeric version of the [Date] value.
[Date] is not the Release date, [Date (release)] is the Release Date, and again is fully qualified.
If [Date] is provided but [Year] is not, MC sets [Year] to the year included in the [Date] metadata. If [Year] is provided but [Date] is not, MC sets [Date] to just the year in the [Year] metadata. They are linked fields. In fact, the [Year] field is defined using the Expression "FormatDate(Year)&DataType=Integer". So you can see [Year] is an integer value, not a date or string value. It is a whole number only.
Have a look at all the date field MC provides in "Options > Library & Folders > Manage Library Fields".
BIS are doing it wrong if they only provide Day and Month in the Date tag.
Or your Views are formatted to show just Month and day.
Search the forum for "Release Date" and similar, and see what you can learn.
