The current generation of on-board engine monitoring equipment downloads real time (or at worse at the end of every flight) - and the engine companies process that with fancy computer algorithms that can predict failures before they happen and alert the operator they need to get an engine off-wing before it actually fails.
In this case, unfortunately, this did not happen. My understanding is even after the engine failed to start, Rolls Royce could not offer any data that pointed to the cause of the failure. There were none of the parameter shifts that indicate a pending or existing problem. Thus a period of troubleshooting, including a boro, was necessary before the evidence lead to the requirement to replace the donk.