Need a checker cell to look at the first 4 letters in each cell in a range for duplicates

I'm looking to create multiple rosters for events. I'm looking to have one cell that looks at a range of cells and checks to see if any of the range's cell values are duplicates with the same first four letters. I have a base CountIf that I'm building off of, which works to look at one cell's first 4 letters compared to a range. This is close but I want one cell that looks at the whole range for duplicate first 4. It's meant to be a checker cell that indicates I've put the same person down for a roster twice.

=IF(COUNTIF(A:A,LEFT(A2,4)&"*")>1,"Duplicate","")