Not copying duplicates

Hey guys,
So I have this code here written that takes the selected area and copies it for me based off the cells that I want the values from. How do I check to see if the values that are being copied already exist to where they are being pasted to.
As an example lets say its coping John (Cell F), and 29 (Cell Q)
Its going to post at the first empty cell of text from B39 from top down. How can I get it to check above the first empty cell to see if John is already listed and 29 is already listed?
Have I taken the wrong approach on this?

Sub Completed()

Dim datasheet As Worksheet 
Dim reportsheet As Worksheet
Dim finalrow As Integer
Dim i As Integer 'row counter



Set datasheet = Sheet1
Set reportsheet = Sheet1

datasheet.Select
finalrow = Range("E" & Rows.Count).End(xlUp).Row

For i = 2 To finalrow
    If Cells(i, 17) <> "" And Cells(i, 17) <> "Completed Date" Then
    Application.Union(Cells(i, "F"), Cells(i, "Q")).Copy
    reportsheet.Select
    Range("B39").End(xlUp).Offset(1, 0).PasteSpecial xlPasteFormulasAndNumberFormats
    datasheet.Select
    End If
Next i


reportsheet.Select
Range("B2").Select

End Sub