OK, you have your bases covered, and evidently your company chooses to simplify things with the protocol you describe. This has, I guess, the advantage of forcing the highest Vmcg and Vmca so you don't have that to worry about.
But the fact is, you can apply reduced thrust to any certified rating, including Derates 1 & 2.
There's a bit of history behind this: Say an early model airplane is delivered with engines rated A, and later an upgrade to B is offered. The A rating is permitted to use flex thrust down to a 25% reduction. When B engines are installed, the A rating is still valid, including its 25% reduction. This has occurred many times over the years.
EDIT: My upper management once embarked on some "housecleaning", and planned to remove the old engine A rating from the type certificate data sheet. We flight ops people saw the folly in this, especially the effect on contaminated r/w ops. I wrote the letter that got this plan buried.
Last edited by barit1; 24th Nov 2009 at 23:15.