[QUOTE=
As per the "B" model, which had more powerful Pratt and Whitneys than the "A" and had a more robust gearbox (a thirsty machine). There was then the C model, with smaller engines for economy, coupled with the B gearbox. And commonly known as the "B minus".... at least you only had the engine limits to worry about in those.[/QUOTE]
And of course Nr for the B and C models was increased from 100% to 107%
It's not unusual to bump up the Nr during original development and/or for followon models, with or without a change in engines.