Bearfoil
Let me propose a scenario that might be appropriate for the Trent 900 situation today.
Generally, engine manufacturers that develop, test, gain type certification and go through a multi-aircraft certification program do not stop at the conclusion and move on to the next engine. In fact, there is much more to be learned to be passed back to design engineers, performance engineers and the service business arm such as Rolls Royce's "Total Care". Usually an engine is reserved in a test cell where a cyclic program is run to simulate "the life of the engine". One or two other engines are available initially to run special cycles to examine component improvements or even new components. Why? Because the money to be made comes from the engine services, not the original build and sales of the engine itself. I don't think this is what you would call a "long runway engine program" where thousands of engines will be built so services is where the money will be made. Data from the "life of the engine" and planned periodic teardowns of this engine becomes the basis for refinement of design practices, comparison of performance over time real verses design theoretical, and most important, the criteria for establishing long term service contract costs. It behooves the engine manufacturer to improve all the components or systems in the engine to be capable on wing for 5 or 6 years enabling a profit to be made as part of the "Total Care" program while more accurately setting the per hour fee to future engine users. That all said, here is what I think happened to Rolls Royce on the Trent 900 Qantas engine.
One way to look at it is this way: (A) leads to (B), (B) leads to (C), (C) leads to (D) and (E) leads to failure. This is the classical failure methodology of a complex system. Looking at engine #2's failure,
(A) = Unknown
(B) = Unknown
(C) = Unknown
(D) = Stub pipe
(E) = IPT Disc burst/major engine failure/damage to aircraft
The trick is to identify (C), (B) and (A), (A) being the root cause.
From the aircraft flight certification program and the "cyclic Life of the engine" testing, I think Rolls Royce found some results (B) & (C) that didn't match original design life analysis theories and were in the process of making corrections. But the stub pipe failure, either Mfg. defect or wear, came much sooner than anticipated, if anticipated at all. If (B) & (C) could have been incorporated in engine #2, perhaps the failure could have been prevented. I don't know. Has the true root cause (A) been identified? I don't know, perhaps this is in the newest "C" mod. all the operators are wanting ASAP.
Turbine D