I think you are confusing 'unclassified' and 'declassified': declassified means that it was previously (but no longer) classified; unclassified means that it is

I think you are confusing 'unclassified' and 'declassified': declassified means that it was previously (but no longer) classified; unclassified means that it is not classified. If this had been classified then declassified it would have the original marker (but crossed out), and the text at the bottom would be "Declassified and Approved for Release", rather than just "Approved for Release". For an example of this, see https://www.nsa.gov/public_info/_files/cryptologs/cryptolog_01.pdf https://www.nsa.gov/public_info/_files/cryptologs/cryptolog_...