I thought that too, but the 777 nose numbers start with 20, 21, 23, 24, 25, 26, 27, 28, and 29. That is a lot more numbers then they have 777 configurations. Same for the 757, they have 4, 5, 6, and 7 as the second number in the nose number on the plane, yet only 3 configurations (ps, ETOPS, standard).