Certificating Authorities, 1936 to 1987.
.......actually, I'm not too sure about the actual validity of the FAI Aviators Certificate - it wasn't the PPL itself from what I can see. Perhaps for use overseas..? (I recall, in the 1970's having to obtain an 'RAC International Driving Licence' to drive abroad...!).
A have a full trail of a deceased friends aviation documents, both flying, PPL and Ground Engineer. Hope this helps;-
Air Ministry Ground Engineers Licence, July 1936. CA Form 9.
FAI Aviators Certificate, granted August 1939.
Air Ministry PPL CA Form 64, August, 1939.
Ministry Of Civil Aviation Aircraft Maintenance Engineers Licence CA Form 9. July, 1946.
UK Ministry Of Aviation Student Pilots Licence CA Form 602. May, 1961 (As a returnee.)
Ministry Of Aviation, Aircraft Maintenance Engineers Licence, CA Form 612. December 1964.
Civil Aviation Authority, Aircraft Maintenance Engineers Licence, CA Form 1703. August 1977 - 1987.