XL 2013 Problème format Date sur Excel

Option Explicit

Sub convertDate()
   Dim dl As Long, I As Long, cell As Range, Rng As Range, Ws As Worksheet
   For Each Ws In ThisWorkbook.Worksheets
      If Ws.Name <> "RECAP" Then
         With Ws
            dl = .Range("A" & Rows.Count).End(xlUp).Row
            Set Rng = .Range("H4:J" & dl)
            For Each cell In Rng
               If Not IsDate(cell) Then
                  cell.NumberFormat = "General"
                  If Len(cell) = 8 Then
                     cell = Mid(cell, 3, 2) & "/" & Left(cell, 2) & "/" & Right(cell, 4)
                  Else
                     cell = Mid(cell, 2, 2) & "/" & Left(cell, 1) & "/" & Right(cell, 4)
                  End If
               End If
            Next
            Rng.NumberFormat = "m/d/yyyy"
         End With
      End If
   Next Ws
   MsgBox "Fin de traitement des dates!", vbInformation, "DATE CONFORME"
End Sub