Yes I am an Examiner. An Instructor can't do the check because only an Examiner can sign the SRG1119. However if you do the flight with an Examiner, Revalidation or higher then they can sign the form and the Language Proficiency Certificate.
As long as your licence says English Proficient I would not bother about anything else, it will work itself out in the wash. Next time you do a 2 year flight and get an Examiner to sign your licence ask them to complete the level 6 if you are really that worried. It is not really needed and as I said you will get nothing back from the CAA to note the change.
It is all a bit of a dogs dinner really. Don't worry about it!!!