I agree, and I am not aware of any cases of this having come forward (although, to be fair, they cannot declassify a non-record). The notion comes from the fac

I agree, and I am not aware of any cases of this having come forward (although, to be fair, they cannot declassify a non-record). The notion comes from the fact that the response is supposed to be fundamentally different from saying, "those records are classified," which is totally allowed by FOIA. The very reason for the existence (and general acceptance) of Glomar responses is that they do not confirm the existence of the records. So what that means is that a Glomar response could be made to a request for which the records do not exist.