Add an Additional Filter to ComboBox1

Hi all,
I have the following code below that provides me a combobox with unique values; however, I'd like to be able to add an additional filter from column A such as showing only values that have been added or moved instead of all of them.
Thanks for your help.

Private Sub UserForm_Initialize()
Dim myCollection As Collection, cell As Range
On Error Resume Next
Set myCollection = New Collection
With ComboBox1
.Clear

'loop thru
For Each cell In Range("O18:O" & Cells(Rows.Count, 15).End(xlUp).Row)

If Len(cell) <> 0 Then
Err.Clear
myCollection.Add cell.Value, cell.Value
If Err.Number = 0 Then .AddItem cell.Value
End If

Next cell

End With

End Sub