Maybe there was a feature update since when the line closure is model and not fleetgroup based but somehow he forgot to edit all sentences in the manual.
You should make a bug thread about his! Like simply copy this thread in the bug forums.
And np for the aircraft data.
Edit: When nobody wants 717 at all, the line is closed completely. When people want ATR 42-300, the ATR 72-200 line could be closed. I guess the 717 hasn't sold well in both variants.