Trent 970/Trent 972:
Could it be that both are one and the same engine but subject to a different maintenance regime?
For example, I had good experience of the General Electric CF6-50C2. The basic engine would normally produce about 4,000 lbs of extra thrust above its guaranteed minimum. If an operator wanted to make use of this extra thrust benefit for performance purposes, then that operator could opt to go for the C2B option.
This was fine and it meant that they could operate, for example, at higher operating weights but the downside was that since the engine was now on a different maintenance cycle, then components were going to have to be changed more often.
I was told that the only modification to the engine was to change the "plate" on the engine which took about five minutes to do.
If this has nothing whatsoever to do with the case in hand then I apologise in advance!