Get stored value from existing item in dictionary

I'm not sure exactly what the results should be, but if you store the row number "i" as the item, instead of the key then you can use that row as the Datum for copying down, based on each "Key", as shown in the "Else" statement.
Try the code below for results on sheet2.

Sub MG20Jul58
Dim a, dic As Object, s As String, i As Long, j As Long, col As Variant, Ray, n As Long
   
    a = ThisWorkbook.Worksheets("Sheet5").Range("A1").CurrentRegion.Value
    a = Application.Index(a, Evaluate("ROW(1:" & UBound(a, 1) & ")"), [{3,7,13,14,15,16,17,18,19,20,21}])
   
    Set dic = CreateObject("Scripting.Dictionary")
    dic.CompareMode = 1

    For i = LBound(a) To UBound(a)
        s = a(i, 1) & vbTab & a(i, 2)
        If Not dic.Exists(s) Then
            dic.Add s, i
           
            For j = LBound(a, 2) To UBound(a, 2)
                If j = 1 Or j = 3 Or j = 6 Or j = 9 Then
                    If i > 1 Then a(i, j) = CLng(Application.WorksheetFunction.WorkDay(CDate(a(i, 1)), IIf(j = 1, 0, Val(j / 3))))
                End If
            Next j
        Else
            
            For n = 1 To UBound(a, 2)
                a(i, n) = a(dic(s), n)
            Next n
        End If
    Next i

Sheets("Sheet2").Range("A1").Resize(UBound(a, 1), UBound(a, 2)).Value = a

Regards Mick