Given that document, this is all the code you should need.
Code:
Private Sub Document_ContentControlOnExit(ByVal CCtrl As ContentControl, Cancel As Boolean)
Application.ScreenUpdating = False
Dim i As Long, StrOut As String
With CCtrl
If .Title = "Job" Then
Select Case .Range.Text
Case "ABC01"
StrOut = "Joe Smith,Cindy Lou"
ActiveDocument.SelectContentControlsByTitle("Reference").Item(1).Range.Text = CCtrl.DropdownListEntries(2).Value
Case "XYZ02"
StrOut = "John Doe,Jenny Lee"
ActiveDocument.SelectContentControlsByTitle("Reference").Item(1).Range.Text = CCtrl.DropdownListEntries(3).Value
Case "GEF03"
StrOut = "Jack Handy,Jill Foote"
ActiveDocument.SelectContentControlsByTitle("Reference").Item(1).Range.Text = CCtrl.DropdownListEntries(4).Value
Case Else
ActiveDocument.SelectContentControlsByTitle("Reference").Item(1).Range.Text = vbNullString
End Select
With ActiveDocument.SelectContentControlsByTitle("CM")(1)
.DropdownListEntries.Clear
For i = 0 To UBound(Split(StrOut, ","))
.DropdownListEntries.Add Split(StrOut, ",")(i)
Next
.Type = wdContentControlText
.Range.Text = ""
.Type = wdContentControlDropdownList
End With
End If
End With
Application.ScreenUpdating = True
End Sub