Validar apenas mes e ano

Function ChecaMesAno(Data As String) As Boolean
'FUNÇÃO PARA CHECAR SE DATA É VÁLIDA
'FORMATO DE ENTRADA DA DATA: MM/AAAA

'SAÍDA: ChecaData = TRUE - DATA VÁLIDA
' ChecaData = FALSE - DATA INVÁLIDA

    ChecaMesAno = True

    If Len(Data) <> 7 Then
        ChecaMesAno = False
        Exit Function
    End If
    Dim X As Integer
    Dim erro As Boolean
    erro = False
    For X = 1 To Len(Data)
        Select Case X
            Case 1, 2, 4, 5, 6, 7:
                If Not IsNumeric(Mid(Data, X, 1)) Then
                    erro = True
                    Exit For
                End If
            Case 3:
                If Mid(Data, X, 1) <> "/" Then
                    erro = True
                    Exit For
                End If
        End Select
    Next
    If erro Then
        ChecaMesAno = False
        Exit Function
    End If
    Dim Mes As Integer
    Mes = Mid(Data, 1, 2)
    If Mes < 1 Or Mes > 12 Then
        ChecaMesAno = False
        Exit Function
    End If
    If Val(Right(Data, 4)) < 1900 Then
        ChecaMesAno = False
        Exit Function
    End If
End Function

Public Sub CampoData_MesAno_Change(ByRef oControle As Object)
        Dim X As Byte
        Dim AuxStart As Byte
        Dim AuxData As String
        AuxStart = oControle.SelStart
        AuxData = ""
        For X = 1 To Len(Trim(oControle.Text))
            If Mid(oControle.Text, X, 1) <> "/" Then
                AuxData = AuxData & Mid(oControle.Text, X, 1)
            End If
        Next X
        Select Case Len(Trim(AuxData))
            Case Is < 3: oControle.Text = AuxData
            Case 3: FlagData = False
                    oControle.Text = Mid(AuxData, 1, 2) & "/" & Mid(AuxData, 3, 1)
            Case Is > 3: FlagData = False
                         oControle.Text = Mid(AuxData, 1, 2) & "/" & Mid(AuxData, 3, 4)
        End Select

        Select Case AuxStart
            Case 3: oControle.SelStart = 4
            Case Else: oControle.SelStart = AuxStart
        End Select
End Sub