Option Explicit
Sub Remplir_Dates_Manquantes()
Dim i As Integer, DerL As Integer
DerL = Range("A65000").End(xlUp).Row
'Application.ScreenUpdating = 0
Range("A1:A" & DerL).Sort Key1:=Range("A1"), Order1:=xlAscending
On Error Resume Next
For i = DerL To 2 Step -1
If Cells(i - 1, 1) + 1 <> Cells(i, 1) And Cells(i - 1, 1) <> Cells(i, 1) Then
Cells(i, 1).EntireRow.Insert
Cells(i, 1) = Cells(i + 1, 1) - 1
i = i + 1
End If
Next i
End Sub