I thought the different lengths were just for the down tube and seat stays. Top tubes were all 600mm and seat tubes were all 635mm.
"Composition A" for frame sizes up to 57cm, down tube = 600mm, seat stay = 500mm
"Composition B" for frame sizes 58cm to 61cm, down tube = 620mm, seat stay = 550mm
"Composition C" for frame sizes 62cm to 65cm, down tube = 635mm, seat stay = 580mm