Obviously they had to stop using this protocol once all the sensible names had been used up.
Airbus ran a similar system...
A3 TWO 0 two engines
A3 FOUR 0 Four engines
the A330 was originally designed to have 3 engines originally!
They now have the A380 to keep their "middle digit" one higher than boeing's (777) after advice from their marketing department said it made the aircraft sound more advanced.
Max