To illustrate my problem, sample code given below:

set oEx = New Excel.Application
set oBk = oEx.Workbooks.Open("MyBook.xls")

dim oSh as Excel.Worksheet
For Each oSh In oBk.Worksheets
Debug.Print oSh.CodeName
Next

Sometimes I could not refer to the codename of worksheet. After I
intentionally create a tiny macro in the "MyBook.xls" and delete it, I could
refer to the codename of the sheets by the above code. I need to always
refer to the codename in my current project. Someone knows how?