B787-9 pilot reported right engine vibration indication exceeded limits. Pilot learned after landing that a blade in the N2 section had been ejected and damaged other blades in the engine.

Narrative

On initial descent into ZZZZ; all of our engine instruments populated on our display. This is an indication that one of the parameters has exceeded its limitation. The right engine N2 Vibration Gauge showed a value of 4.3 units. 4.0 units is the limitation. When the engine was at idle; it showed 3.6 units. The left engine was showing 0.5 unites for comparison. All other engine parameters were the same between the two engines. A flight attendant reported hearing some noise on the right side of the aircraft. This happened while on the arrival and there was not enough time to troubleshoot further. We landed without incident and wrote up the excellence in the logbook. We found out two days later that a turban blade in the N2 section of the right engine had been ejected out the back of the engine; damaging multiple other blades in the process.I believe we did everything correctly given the information we had. Our only indication was the vibration gauge and a report from the back of some noise on the right side of the aircraft. There is an ENG LIMIT EXCEED L; R checklist; but that appears when other parameters are exceeded. I believe the vibration gauges are for trend and informational purposes. There are no checklists in the unannunciated section of the QRH for engine vibration. Given the short time remaining in the flight; I believe the best course of action was to just land the plane; and we did just that. No other engine limitations were exceeded and I believe this is just a case of metal fatigue.