Try this macro.
Sub Test()
Sheets("Data").Activate
Sheets("Summary Sheet").Rows("2:65536").Clear
For N = 2 To Cells(65536, 1).End(xlUp).Row
If Application.CountIf(Sheets("Summary Sheet").Columns(1), Cells(N, 1)) = 0 Then
Sheets("Summary Sheet").Cells(65536, 1).End(xlUp).Offset(1, 0) = Cells(N, 1)
TargetRow = Sheets("Summary Sheet").Cells(65536, 1).End(xlUp).Row
Else
TargetRow = Sheets("Summary Sheet").Columns(1).Find(Cells(N, 1), , xlValues, xlWhole).Row
End If
Sheets("Summary Sheet").Cells(TargetRow, 256).End(xlToLeft).Offset(0, 1) = Cells(N, 2)
Next N
End Sub
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