Every now and again, particularly in the PDF files covering equipments, you will see a scanned page bearing a Security Caveat.  None is higher than RESTRICTED so there is nothing shocking in terms of security lapses.  Moreover, with only a very few exceptions,  documents so marked were given that security marking in the 1950's.  Thus, it is reasonable to believe that some  fifty years on, the lowliest of the classifications, viz, Restricted, is now de-classified to the level of "public domain" awareness.