Some fields on a control record are a live/shared field. When it is updated in the control record the changes flow through to any linked test forms that include that field, regardless of the audit year. 

When a test torm is marked as completed, any modification on this live/shared field should have no impact on the closed form. The information that should remain on the closed form shoulf bw the one that existed on the control record at the moment of the form closure.