You used the word “legally”, so let's go to the context of a court, where someone didn't show up when subpoenaed at a certain time. There are excuses and there are explanations. An explanation acceptable to the court might be, “I got hit by a car and I was in hospital.” You were caught in traffic? That might not work so well. So there are explanations and there are excuses. It's the court's judgment as to whether the explanation is sufficient. What that suggests is there should be an opportunity provided for the person to explain why they didn't attend. So another day is set, and the first question that might be asked of the individual is, “Why weren't you here the last time we summoned you?” It would give the individual an opportunity to explain, and then the committee could make its own judgment as to whether that's sufficient for its purposes.
On June 15th, 2010. See this statement in context.