I don't know about the S76, but some time ago Rolls Royce came out with a requirement to have a sticker on the instrument panel in Bell 407s stating the need to avoid steady state operations between 68% and 86% NG. They have recently amended this to a more accurate set of numbers, something like 68.6% to 87.4%, like I'm going to pay that much attention.
I have asked people in the know and can't get much of an explaination as to why things have changed.