Macro changement de date en fonction d'une cellule dans une suite de dates.

Option Explicit
Private Sub CommandButton1_Click()
For_X_to_Next_Ligne
End Sub
Sub For_X_to_Next_Ligne()
Dim FL1 As Worksheet, NoCol As Integer
Dim NoLig As Long, Var As Variant
Set FL1 = Worksheets("Feuil1")
    splitcolonne
    NoCol = 2 'lecture de la colonne B
    For NoLig = 2 To Split(FL1.UsedRange.Address, "$")(4)
        Var = FL1.Cells(NoLig, NoCol)
     If FL1.Cells(NoLig, NoCol) = FL1.Cells(NoLig - 1, NoCol) Then ' si la valeur est égale à la ligne précédente
      FL1.Cells(NoLig, NoCol - 1) = FL1.Cells(NoLig, NoCol - 1) & "(+1)" 'on ajoute (+1)
      End If
      Next
    Set FL1 = Nothing
     Columns("B:B").ClearContents 'on nettoie colonne B
End Sub
Sub splitcolonne()
Dim FL1 As Worksheet, NoCol As Integer
Dim NoLig As Long, Var As Variant

    Set FL1 = Worksheets("Feuil1")
    NoCol = 1 'lecture de la colonne A
    For NoLig = 1 To Split(FL1.UsedRange.Address, "$")(4)
        Var = FL1.Cells(NoLig, NoCol)
     FL1.Cells(NoLig, NoCol + 1) = Split(Var, "/")(2) 'on met l'année dans la colonne B
      Next
    Set FL1 = Nothing
End Sub