On the Canon Camera Museum site it shows the longest lens in the FD and new FD lineup is 800mm. There is 1200mm in the FL and EF lineups. Did Canon continue the 1200mm FL production during the FD era?
They did for awhile. The FD lens line was introduced late in 1970. Several FL lenses stayed in production until they were eventually replaced by more-modern FD equivalents. I'm not sure when the FL 1200 was discontinued, but it was listed in Canon catalogues as late as 1980.
There is some amazing surf photos shot with this lens during the late 1980's at Sunset. I forget the name of the photographer, but as a media seeking photo enthusiast hardcore surfer I looked over those images carefully many times. I'll see if I can find a link.