If I'm understanding correctly ...
Option Explicit
Sub AddDate()
Dim oSlide As Slide
Dim oShape As Shape
For Each oSlide In ActiveWindow.Selection.SlideRange
For Each oShape In oSlide.Shapes
If oShape.Name = "Dated" Then
oShape.Delete
Exit For
End If
Next
Set oShape = oSlide.Shapes.AddShape(Type:=msoShapeRectangle, Left:=26 * 28.3464567, Top:=0 * 28.3464567, Width:=80, Height:=26.6)
With oShape
.Name = "Dated"
.Line.Visible = msoFalse
.Fill.ForeColor.RGB = RGB(255, 255, 255)
.TextFrame.TextRange.Font.Color.RGB = RGB(0, 0, 0)
.TextFrame.TextRange.Characters.Text = Format(Now, "Short Date")
.TextFrame.TextRange.Paragraphs.ParagraphFormat.Alignment = ppAlignCenter
.TextFrame.TextRange.Paragraphs.ParagraphFormat.SpaceBefore = 0
.TextFrame.TextRange.Paragraphs.ParagraphFormat.SpaceAfter = 0
.TextFrame2.VerticalAnchor = msoAnchorMiddle
.TextFrame2.TextRange.Font.Size = 10
.TextFrame2.TextRange.Font.Name = "Arial"
.Rotation = 0
End With
Next oSlide
End Sub