To prevent recurrence, tell the pilots to count the rivets on the particle bypass doors during the pre-flight. If they can't count them, then tell them to remove the inlet plugs.
Although this seems like an easy one to avoid, once you're seated in the cockpit it's not an easy one to diagnose. Failure to light may be the only symptom you notice, so you go through a dry run then a second start attempt. Maybe you even decide to try the other engine to get a generator online before you go through that process on the first engine. Point is, its a simple cause but can lead to costly outcome.