Date format issues

Using your original sample and Power Query

Here is the Mcode and file for your review.

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}}),
    #"Inserted Year" = Table.AddColumn(#"Changed Type", "Year", each Date.Year([Date]), Int64.Type)
in
    #"Inserted Year"

Power Query is a free AddIn for Excel 2010 and 2013, and is built-in functionality from Excel 2016 onwards (where it is referred to as "Get & Transform Data").

It is a powerful yet simple way of getting, changing and using data from a broad variety of sources, creating steps which may be easily repeated and refreshed. I strongly recommend learning how to use Power Query - it's among the most powerful functionalities of Excel.

- Follow this link to learn how to install Power Query in Excel 2010 / 2013.

- Follow this link for an introduction to Power Query functionality.

- Follow this link for a video which demonstrates how to use Power Query code provided.