As I said that's why. If you add the number to anything other than the placeholder either manually or with code the overspill pages don't see it.
You might need to enter SOME text in the textbox and leave the number in the placeholder.
Try this:
Sub notesmaster()
Dim sLvModNum As String
sLvModNum = "1200xyz"
On Error Resume Next
With Application.ActivePresentation.notesmaster.Shapes
.Item("newtext").Delete
Dim oNum As Shape
Set oNum = getSN(ActivePresentation.notesmaster)
If oNum Is Nothing Then Set oNum = _
.AddPlaceholder(ppPlaceholderSlideNumber)
If Not oNum.TextFrame.TextRange Like "Overspill*" Then _
oNum.TextFrame.TextRange.InsertBefore ("Overspill ")
With .AddTextbox(msoTextOrientationHorizontal, oNum.Left, oNum.Top - 20, oNum.Width, 20)
.Name = "newtext"
With .TextFrame.TextRange
.Text = "Module " & sLvModNum
.ParagraphFormat.Alignment = ppAlignRight
.Font.Size = oNum.TextFrame.TextRange.Font.Size
.Font.Color = oNum.TextFrame.TextRange.Font.Color
End With
End With
End With
End Sub
Function getSN(oNM As Master) As Shape
oNM.HeadersFooters.SlideNumber.Visible = True
For Each getSN In oNM.Shapes
If getSN.Type = msoPlaceholder Then
If getSN.PlaceholderFormat.Type = ppPlaceholderSlideNumber Then 'found it
Exit Function
End If
End If
Next
End Function