Actually, there's a pretty nifty native way to do this. Probably less efficient than a hash lookup, but more consistent.

Function MyMonthName(ByVal m As Long, Optional ByVal appr As Boolean =
+ False) As String
   Dim v
   v = CDate("2004-" & m & "-01")

   Dim fmt As String
   If appr Then
      fmt = "MMM"
   Else
      fmt = "MMMM"
   End If

   MyMonthName = Format(v, fmt)
End Function
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