Assuming that the engine fuel feeding system is symmetrical and was isolated between the two of them, I can presume we have only one anomaly that was replicated between the 2 existing engines; IMHO I believe that if this 777 had 4 engines all of them would have suffered the same problem (whatever it may be), and I would guess that the timing between failures would be very close.
This anomaly exists, it’s real, and if it has the ability to affect 2 separate engine/tank systems in the very same time-frame, it’s possible to replicate it for testing purposes. It will happen again.