Sub Unione()
Dim Wks1 As Worksheet, Wks2 As Worksheet, uRigaWks As Long, i As Long
Dim Sh As Worksheet, uRiga As Long, j As Long

Set Wks1 = Worksheets("Baseline")
Set Wks2 = ActiveSheet

uRiga = Wks1.Range("A" & Rows.Count).End(xlUp).Row       'ultima riga - solo righe visibili
'uRiga = Wks1.UsedRange.Rows.Count                       'ultima riga - anche righe nascoste
Wks2.UsedRange.ClearContents

Wks1.Range("A1:A" & uRiga).Copy
Wks2.Range("A2:A" & uRiga + 1).PasteSpecial xlPasteValues
Wks2.Range("A2").Select
Application.CutCopyMode = False
uRiga = uRiga + 1

For Each Sh In Worksheets
    If Sh.Name <> Wks1.Name And Sh.Name <> Wks2.Name Then
        With Wks2
            uRigaWks = Sh.Range("A" & Rows.Count).End(xlUp).Row
            'uRigaWks = .UsedRange.Rows.Count
            For i = 2 To uRiga
                For j = 1 To uRigaWks
                    If .Range("A" & i).Value = Sh.Range("A" & j).Value Then
                        .Range("B" & i).Value = Sh.Range("B" & j).Value
                        GoTo prossimo
                    End If
                Next j
prossimo:
            Next i
        End With
    End If
Next Sh
MsgBox "Done!"

Set Wks1 = Nothing
Set Wks2 = Nothing
End Sub